sanjay.debian

I hear this humming noise coming from somewhere rear end of my car. First I thought it must be a wheel bearing. But I had my rear passenger side bearings replaced just last year and if I remember correctly, the noise did not sound similar to the noise now.

Also the noise is not present when the car is moving at slow speed. It becomes noticeable around 30 mph and peaks around 35-40 mph. After 50 mph, I don't think I hear anything. My CEL is also lit with a lean code (don't remember the exact code).

So what do you guys think it is? wheel bearing? fuel pump? something else? Thanks.

Kris Hansen

I had a noise like that on my A6, turned out to be the antenna.. hopefully yours is something silly like that.

You might try rotating the tires, checking the brakes, and if you can, have the fluid level in the rear differential checked.

Could be pretty much anything.

sanjay.debian

Thanks Kris. How would one check fluid level in rear differential?

MartinH

If it is like my 2.8, there is a level/fill plug on the right side of the rear diff. This was a real pain to undo on my car due to corrosion. Suggest you spray it with PB Blaster for a few days beforehand. If there is no or little sign of an oil leak around the seals, then low oil shouldn't be a problem.

jimrobertson

This is classic wheel bearing noise. Could be the one you didn't replace. Cross rotating your tires will narrow it down.As for your code it is likely unrelated.There is a code guide in faq isn't there?

Kris Hansen

Yep, and I've actually had a few wheel bearings fail where the INNER row was bad, and the noise was slightly different, and, it didn't change with corner loads like if the outer row was bad.

sanjay.debian

Thanks all for your help. I just noticed this, trying to diagnose another problem.

<img src="http://i600.photobucket.com/albums/tt84/parshv/IMG_0003-1.jpg">


The metal piece that holds exhaust pipe to frame became disjointed somehow. So may be the entire exhaust is reaching its resonance at 35-40 miles an hour causing the humming noise.

Could any of you please post a pic of that section? I am not sure whether I need to just weld it or if something else has fallen off.

Please post a pic. Thanks.

sanjay.debian

Never mind, I found a picture right here on audiworld.

rhelaur

Was it the problem with the exhaust pipe causing the humming noise? I have an A6 - Automatic and there is a humming noise which always kicks in over 45 kph. Mechanic is having trouble identifying the cause and has suggested changing the tyres or replacing rear brakes which are hard....

sanjay.debian

No I haven't had any success in identifying the noise as well. I did think it was the exhaust. But seems like it is not.

Also the speed threshold has changed for me now. It used to get loudest at the speed of 40 miles an hour, now it gets loud at 50 miles an hour.

Let me know if you figure out what's wrong with yours. Thanks.