Q&A

 Master

It can be hard to distinguish between a faulty rear wheel bearing or tire noise. You can try rotating the tires to see if the noise moves to the front. It is also possible to listen to the bearings with a stethoscope with the car on a hoist and the wheels turning. Wheel bearing or tire noise would not normally occur only when accelerating or decelerating. You may need to road test your 1999 Audi A4 Quattro with a qualified technician to help try and determine the cause of your noise.

 Journeyman

rear wheel bearing is my bet from experience. if you can, safely try swerving moderately left to right when noise is heard. if the noise changes, most likely a bearing. tire noise can be ruled out if noise is the same on various roads (like dirt). the proper "audi" bearing has blue seals. there is often confusion in the parts manual from audi.

Not right rear but center rear. I had this problem for a time until i figured it out. Rear differential most likely the culprit. It most likely leaked its oil (95 heavy weight) through one of the rear cv joints. I refilled through the allen wrench bolt on the rear of the rear differential. Problem solved! Sorry 6 months late!