I have a chipped 2002 A4 avant with new intake and exhaust. Not a very experienced car guy but have always loved Audi's and absolutely love my ride. Over the last week began hearing a humming type noise from under mid-section of car. Doesnt matter if I am moving or not and when I hit the gas the noise may change pitch slightly but does not go away. I suspect it may be the exhaust. Maybe part of the exhaust is touching the frame creating the humming? Any help or insight would be greatly appreciated. Thanks in advance.

 

Sounds like exhaust, especially being aftermarket. Could be anywhere along the exhaust including something as simple as a heat shield. If it makes the noise even at idle, the best thing to do would to get it on a hoist and get under it. You'll find the noise pretty quickly and be able to remedy it. If you don't have access to a hoist, any muffler shop should be able to do it. If anything they will be able to let you know if it is the exhaust or not by process of elimination.

Tony

 

is it droneing or humming.. if its humming sounds like something to do with bearings.. wheel bearings, center support bearings etc etc... if its droneing sounds like lots of other stuff as mentioned above also cheak exhaust hangers those will rattle if broke and stuff like lose bolts from dp or testpipe to exhaust etc

 

If it were bearings it would stop when the car is stationary, so that cant be it.
If your not mechanically inclined i would take it in to get checked by a trusted independent audi/vw mechanic. if its from the transmission (also applies to driveline, differentials etc), you need to fix it now, waiting can make it much, much more expensive. if nothing is visibly amiss checking the oil in the tranny/ differential will give you a good indication of their health. Sometimes a dying fuel pump will hum loudly before it goes completely, but i suspect your right about the new exhaust being the culprit.
hope this helps

 

Thanks everybody. The noise had stopped for a couple of weeks then reappeared. I took it to an Audi dealer and they diagnosed a stuck fuel pump valve. They fixed it for about $200.

Now, on to my next noise. A rattling coming from under the engine. Sort of sounds like knocking, especially when the engine is turned off. Any suggestions?
Thanks guys!

 

I'd check all the suspension ball joints, rod ends etc. first, and look for any loose heat shields or broken/loose exhaust or engine/transmission mounts at the same time.

 

My A6 2.7T is doing this too! it's at the garage now, and we're testing things. What's different from your sound is that mine will only hum under load - meaning not on the hoist.

Hopefully this is the problem with mine too. The garage mentioned it could be a leaky turbo in the worst case scenario... I hope it's not that... yikes.

Anyways, thanks for your post.