Could be a bearing going bad.
Bad wheel bearing
There can be a slight humming noise while driving a neon. This sound could come purely from the engine to indicate that it is running.
bad wheel bearings will do that, usually in the front.
No. The loud humming noise could be a wheel bearing going bad and it could damage the ABS sensor if allowed to continue.
it does that because it has a generator which makes the engine makes these sounds
I have heard that if you have papers or napkins in the glove compartment box they can get sucked into the air vent which then makes a humming noise that you can hear while driving and as you increase the speed the pitch of the noise gets louder.
If the noise gets louder with speed, it is possible that the bearing in one or more of your wheel hub assemblies have failed. The noise will also become more pronounced during steady state corning.
Could be your cooling fan. And depending on what year your car is, you could have two cooling fans. My cavalier did the same thing. The fan would try to go on when the car heated up, but couldn't. I heard a distinct humming noise with it. It didn't cause any problems until I got stuck on the highway in the summer and my car almost overheated. Take it to a service station.
There are a couple of reasons why a 2001 Audi would make humming noises from the back while it is being driven. The first thing to check is the tires. If the tires are fine, check the wheel bearings.
most common is wheel bearings
tie rods
While rectification pulsations are caused due to ac not being converted to dc perfectly. This causes hum (low frequency humming noise). To smooth these pulsations filters are used. Noise is an unwanted signal in the communication system.