Its most likely a wheel bearing, I had the same problem about a year ago.
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.
it may be a a bad front wheel hub bearing or the brake calliper piston.
its probably your radiator
Your engine might make a humming noise near the alternator after you shut it down because the fan is still running or because the fuel pump is shutting down. Another cause for the humming noise could be the AC motor turning off.
Started with turning right now it's while driving and it's not a constant noise. Just started today
Typicaly, the vibration could be caused by a weak or failed motor-mount. Also, a loose exhaust system with weak or broken mounting points could also be the culprit. Check with your local mechanic. Usualy, they won't charge you to take a peek.
if it is when u are driving it might be thr door or the speaker or if it is closer to the front of the car possibly the transmission
Noises are impossible to correctly diagnoise unless you hear them. TAke it to a good diagnoistition.
most likely a wheel bearing, but im having trouble as well lol. i have the classic wheel bearing humm..replaced both left and right bearings and still have the noise..i cant figure it out.
2001 buick lesabr // when recirculate speed doesnt change only make humming sound rest of heater works fine
I have the same problem some times. I found the air filter box vibrating, which was causing the noise. I am looking for the answer to that one.
I had a very loud humming noise coming from my 99' cougar. I talked to many mechanics and nobody knew what it was. I looked it up online and found two sources( listed at bottom) that said it was the idle air control valve. I replaced the part and my car runs great without the horrible loud noise.;