We need some more information to have a chance of hitting this one. Could be a cat under the hood, could be a clogged oil pump, oil, bad lifters or????
What kind of car and what engine? How many miles, and any recent maintenance? how long does the noise last and what does it sound like?
your cv boot has torn and needs replacement
A bad harmonic balancer can cause a knocking noise. The harmonic balancer doesn't actually produce the noise, but it can cause the noise in the engine.
it's probably a rod knocking
many many things, Loose lug nuts which lets wheel make knocking noise. Engine will make a knocking noise if it is really low on oil. Some timing belts make a knocking, slapping noise just before they break.These are just a few examples . Have someone ride in car with you as you duplcate the noise and see if they can determine which part of the vehicle it is coming from.
Having a bad rod bearing could cause a truck to make a loud knocking noise and shake when driving at high speeds. The engine having a coolant leak or an engine timing problem could also cause the knocking noise.
A knocking/clicking noise when making a turn is a sign of a torn CV boot. In this case it's the driver side boot that is torn.
anti roll bar
wierd
because of you
U Joints can certainly make noise after they've started wearing and are dried out. If you have concern about an unfamiliar noise, take the vehicle to a trusted mechanic or even the dealer. It's nearly impossible to tell you what the noise would be from a description like that.
Compressor is unbalanced as the rpm's drop.
== == I do believe if you hear a knocking noise that your crank shaft could be failing. Which means you will need a new engine. Have it checked out. Replace the harmonic balancer they will make a bad knocking noise. When you start it and the oil light goes out and it knocks, this is what is wrong with it.