We bought an Audi A4 -02 Quattro a few months ago. After a few days we heard, and FELT, a noise coming from the end of the car... the best way to describe it is like driving over those white lines on the road. A thick white line. Donk donk donk donk. "Back then" the "donk" only appered when the car was warm, when accelerating and turning the steering wheel at the same time. We Googled it but nothing, not an solution anyway.

After a few more days we saw that the tyre dimension didn't match. The front tires where 225/40/18 and rear 235/40/18. We bought 4 new tires and the sound seemed to be almost gone. The theory then was that the different dimensions made the rear and the front wheelset roll in different speed and creating a tension.
But after a few weeks the sound returned, even worse. Now it doesn't matter if the car is warm or cold, if turning the

steering wheel or not. The problem does not appear when driving - just when accelerating. We have tried to locate the sound but it's hard. It definitely comes from the back, under the backseat probably. You can really feel it when sitting there. A muffled but hard sound - and feel. Sometimes just one DONK, sometimes many DONK DONK in a row.

We don't really know what to do next. My boyfriend is a mechanic, but no one at his job knows either. Not as pleasing.

Our next guess is the rear axle? The differential? We've heard it is suppose to be bullet-proof but... Any guesses? Please!
(Sorry for my bad english, hope you understand anyway)

 

do u have a cel? "check engine light"

 

No. No lights and no error codes

 

It could be a universal joint or a CV joint going bad.

 

We have changes both drive shafts... forgot to write that, sorry. And changed the oil in the diffential

 

Try jacking up the rear end and turn the rear wheels back and forth, and see if you can duplicate the noise.

 

We have tried that... The wheels must be on the ground.

 

This might not help at all but maybe it will check fuel system it could be the pump making noise? maybe your look at the wrong thing you know?

 

Nope, I shouldn't say impossible but... it's not the pump. Also it was just changed to a new one when we bought the car.

The noise is hard and muffle. It really feels when sitting in the back seat and it definitely comes from the rear tyres.

 

it could be the carrier bearing on the main drive shaft from transmission to the rear differential.