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The sound actually emanates from breaking atomic bonds, and the subsequent rearrangement of the crystalline matrix within grains. This change occurs so quickly, that the material produces a pressure wave (sound wave) that you can hear as a popping sound.

Pretty cool, huh!?

Source: B.S. in Material Science and Engineering from The Georgia Institute of Technology

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It can mean many things. most are ment to squeak when the lining materal is getting thin (needs to be replaced) thay do this with a piece of metal that rubs on the disk to make noise ( can cause damage if it not replace in a timely maner).

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Vroom!lol

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It is probably the heat shield that is between the converter and the bottom of the car. It does what the name. They can be a pain to fix properly. I have always tried fixing mine but the "rattling" noise would always return sooner or later. I ended up taking mine off. Plus these heat shields get old and tend to vibrate relentlessly. Best best is to have someone you know take a look and see what they can do.

Yes it is, and it can cost anywere from $80.00 to $200.00 to fix.

It is also possible that the ceramic compount "honeycomb" in the catalytic converter is breaking apart and/or broke loose inside the converter. If this is the case, you *might* fail emissions but it shouldn't hurt anything (other than failing emissions).

http://www.autozone.com/servlet/UiBroker?UseCase=S001&UserAction=viewSimpleDiagInfo&Parameters=info

just buy a clamp for your heatsheild.. its the cheapest and easiest fix.

I fixed my heatshield with a screw gun and some self tapping screws . The shield is spotwelded in place. Find the areas that have came loose and screw, I used 3/8 inch panheads that where galvinized, they hold up to the heat very well and I hav'nt had anymore problems. I did this 2yrs ago and have had no problems.

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Because your brakes, when applied, "straiten" the rotor (disk) from a cockeyed angle. To put it simply, your wheel bearings are worn and while driving, the rotor, wheel and tire are at a slight angle. The "wear indicators" (a small piece of metal attached to the pads on the top) built into the brake pads are temporarily rubbing against the rotor. When you apply the brake, it temporarily returns the group back to where is should be as if it were new, stopping the indicators from touching the rotor.

Thought i should add that if your wheel stops squeaking when you depress the pedal it is usually a sign of ball-bearing wear. The wheel will squeak through braking if the brakes are done, or worn.

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• My first guess is the neighbor's cat trying to get out from underneath the hood. However, if you see no hair, I would question if the oil is getting up to the valves efficiently. I can do a little research, but I would need the engine size, how often you change the oil, what weight oil you use (5w30?) and does the noise come from above the engine or below? Is the noise a heavy knock or more of a tapping? Post a follow-up here, and I'll try to help.
• Replace the PCV valve. I've had similar problems with a Saturn, I even had to replace a whole motor because it consumed too much oil. I discovered that the new engine was doing the same thing. After replacing the PCV, everything was back to normal.
• There is a TSB about cylinder head gaskets leaking on these cars. This kind of leaks can have various symptoms including those that your having.
• Sounds like car has been overheated and has a collapsed piston skirt. This will cause piston slap until piston heat up and expand.
• Synthetic oil is too thin for a used engine. You should use a straight weight oil, like 30W. Sometimes a flex plate on the transmission will develop cracks and make noise when cold (been there). If the oil pressure is low, there could be a knock, which synthetic oil can cause in an older engine because it is too thin. If there is a check valve in the oil filter or a cheap oil filter, it could be letting the oil drain from the oil pump.
• A cold knock is usually caused by piston to cylinder wall excessive clearence. sometime on a quick rebuild .even with spread the piston skirt. you will get a knock. a low down in the engine heavy knock is main bearings. a fast knock is the rods bearing our a cracked piston. a tapping upper niose is valve lifts in a hydraulic lifter engine. in a solid lifter engine you cah adjust the noise out. some time you will have change the rocker arms our resurface. a bearing knock get louder with temperature. pistons expand with tempiture quiting the noise you need any experinced mechanic to tell you what is wrong, in person. long distance diagnose is hard. hold it up to the phone and let me hear it turbo joe.
• It sounds like you're transmission is beginning to collapse. Is it an automatic? If so, you might want a professional mechanic to examine this IMMEDIATELY. If you don't not only will it become undrivable but it could eventually affect the rest of the engine like a series of bombs taking out individual parts. I had a experience very much like what you're describing with a 95 Buick Skylark and by the time it was looked at 2/3 of the engine was destroyed. Good luck!
• Sometimes if you do not change your oil and the oil breaks down into sludge because you didnt change your oil in time you get whats called a stuck lifter and it can cause a loud rocking slapping noise they have engine cleaners that are on the market some aren't so good so choose wisely.
• Oil... and really watch what oil you use... newer hondas and other foeregn jobs have small ports for oil circulation.... well for the oil to return to the bottom... that could cause rod knock... and since the oil isn't going back down right away to get pumped it would cause the rockers to rattle a bit... but when it warms up finally the oil will flo better.... cant remember which company... but if you popped the motor by using the wrong oil they wont cover a damn cent.... even if its only 3 4 months old.
• Ok there right but if u had bad rings 1 the car would smoke and 2 the car wouldn't have power now i had a 94 thunderbird with a 3.8 and i got the same knocking or tapping and it was a ristpin which is located on the piston if you didnt know now most likely if its a tapping noise from the top of the engine it is normally a callapsed lifter which happen you wont lose power and it wont smoke but to cure the noise use a heavy weight oil such as 20/50the tap could also come from rockers if you have a cloged push rod which happens over age it will cause a lack of oil to the top if the engine process of elimination check the rockers make sure there tight and to torque sequence.
• I've had 2 Hondas, and still currently have one of them. I don't think you have anything to worry about. I was reading all of these responses and laughing...The cars run at a higher idle, which is computer driven until the engine is warm. The Vtec kicks in at higher idles (usually 4000+ rpms) but it is also driven by oil pressure. Since the oil is more viscous at colder temps, and the car is running at higher rpms, your are simply hearing some valve noise. Chances are the valves are perfectly fine. Once warm...does the car run ok, I'm guessing yes. The guy that answered saying it's the Transmission...c'mon you can't compare a Buick to a Honda!
• It's because oil, even a multi-grade like 5w30 is still too thick to flow efficiently when cold. Auto manufacturers choose an engine oil "weight" for OPERATING temperatures, not for when the engine is cold. Even a 5 or 0w oil, when cold, is thicker than a 40w at operating temp. This causes restriction in the small orifices in parts such as lifters, which is the most common source of engine tick when an engine is cold. BTW, cold is defined as a temperature less than the oil's effective operating range, 180-250F for example. That said, an oil at room temperature is still too thick. Google it.

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Tire noise can be caused by the tread pattern used on your tires. Off road tires have a deep tread pattern to give better grip on soft surfaces. Change to a road tire.

Road noise can also be caused by worn suspension components, especially the rubber bushes. Check that yours are not worn. They go soggy or split with age.

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It is called pre-ignition, find a friendly mechanic.

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You really are going to need to be more specific. What kind of noise are you talking about? Are you asking why noises come out of the engine while operating normally? Are you talking about an irregular noise that you think could be a problem?

Engines make noise because there is a conversion of one energy to another and since a lot of it is wasted energy conversion we observe "waste energies" if you will. Such examples are heat and sound.

Inside a running engine there is a lot happening. Coolant and oil is constantly distributed throughout the engine and results in radiant heat and sound. Pistons are for ever going up and down, adding more sound. Combustion, which makes the pistons move, adds to the heat and sound. Parts that take this power of combustion and deliver it to the driving wheels are moving parts and add to heat and sound. Everything makes noise. Appreciated properly, all these wasted energies add to the beauty of the beast that is an internal combustion engine.

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Bad torque converter?

Power steering fluid low?

Bad power steering pump?

Bad bearing on any belt driven accesory I.E. Alternator, Water pump, air pump (if any), a/c compressor etc.

Bad wheel bearing?

Bad tire?

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'Knocking' is a technical term for fuel igniting too early in the combustion chamber.

It can be resolved by adding anti knock additives to the fuel or by retarding the timing at the relevant revs. Most modern engines have built in knock sensors that do this automatically.

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This one is fairly simple. Almost 90 % of the time it is because the shock absorbers are worn out, allowing the coil springs to oscillate roughly and hit the chassis of your vehicle.

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you need a new exhaust job. it would probably be nice. lol

Try new tie rods and/or wheel bearing(s).

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Most likely you need a new strut

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Should they squeak? No. on a bike if they squeak you need to lower the break pads so they are inline with your wheel, if you do this and it still squeaks you need new wheels

Can they? Yes, if they are in contact with the rotor (or drum) even when the brakes are not activated. (Does the squeaking change or worsen when you do brake?) Note that this will cause both a significant loss of fuel economy and a rapid deterioration of brake pads and rotors. Look for grit or stuck calipers, and, failing that, consider the possibility of partially activated parking brake shoes (depending on your vehicle) or wheel bearing damage. You could first try applying some graphite based lubricant to the *back* of the brake shoes (never a drop on the surfaces which contact the rotor!!)-- this is sometimes supplied with the pads by the manufacturer so the clips won't squeak against the housing.

Could be a high spot on the disc or if still rust lip on outer edge rotate disc and place flat edge of screwdriver to edge of disc this will dislodge lip clean away all waste when complete ansre assemble brake caliper (all ways use Eye protection when carrying out this job )

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No. It is not normal at all. Go to a mechanic and get their opinion. Engine knocks usually signify severe damage, and driving with it will cause even more damage. Always check your oil as well. Make sure it is clean and topped off. knocking can also sometimes mean you have the wrong octane but most of the time it means your tie rods or connecting rods are worn

A knock at idle however can only be bearings, it would be beneficial to get things looked at right away,

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Usually, if this sound is of very short duration it is because you replaced the filter. The oil filter on your engine has incorporated an anti-drainback valve which, once removed, removes oil from your engine passages that usually remain filled with oil. Upon starting the engine, it may take several seconds for oil pressure to reach normal levels and achieve quiet operation.

Note that on most fuel injected GM vehicles, the engine should not start until acceptable oil pressure is achieved and this noise indicates unacceptable quality of oil is being used.

Many modern engines made by European auto makers (notably MB and WV) require very specific properties in engine oil. Be sure that you are using an oil that meets the manufacturer's specifications.

If you have a Hyundai 4-cylinder engine and the noise lasts for more than about 3 to 4 seconds you may have an internal engine problem. If the noise persists for a few days or longer, consult with a mechanic.

== == On many vehicles with hydraulic valve lash adjustment (hydraulic lifters or hydraulic rockers) you should not change the oil with a warm or hot engine. If you do so, avoid any highway driving until the engine cools down to ambient temperature. Noise may indicate that you are damaging the engine's valvetrain.

it could be of an old beat up engine and a cylinder is bad..when that goes bad so does the ring..if you have that, it must be replaced.. a.s.a.p. i t could be a shortage of oil, transmission fluid, no oil, bad oil.. It is not abnormal for an engine to 'rap' for a few seconds on the first start immediately after an oil change; it takes a moment for the fresh oil to make its way to the valvetrain. If the rap is persistent, the above answer holds good suggestions 1. check the Oil Dip stick to see if you have oil in the engine 2. What does the oil pressure guage say your pressure is on he dash 3. did you recently fill up with gas that is junky may be 4. it could be a spun bearing, if so you will have to get it fix How to check if it is a spun bearing very simple dran the oil out of your truck Check the Bolt that you took out of the oil pan and see if there are small metal flaks stuck to it, also look up in the oil pan bolt hole to see if you see large metal pieces there. pretty simple cure in most cases just add oil to the filter before installation make sure the filter it top-ed off this should minimze the knock to less then a second I agree with the previous answer of topping the oil filter. In addition, if the noise is still present, change the filter again, and spray brake clean into the oil filter nipple. I would change the oil again at this point.

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If a scooter engine is louder than normal if could indicate one of several problems. You should check the oil level straight away, especially if it is a two stroke engine, as lack of oil, especially two stroke can cause major damage to the engine, and if the engine is running dry it would definitely be louder than normal, and could seize if you continue to use it.The most likely cause of the noise is the exhaust. If a hole has developed, due to rust then the scooter will be much louder than normal. You should visually check the exhaust for any damage. You should also check that the exhaust has not come loose at the manifold (where it joins the engine). If it loose you will just need to tighten it. If there is a hole it will need replacing.
You should also take to a scooter dealer or mechanic as soon as possible, as they will be able to find out what is causing the noise, and they will be able to repair it.

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