I ve got a 97 a4 quattro 2.8 and everytime i pull off from a complete stop (like at a stop sign) i here this wierd slipping/grind in the back by the rear diff ive changed wheel bearings so far, any techs with tips please help!!!!!

 

Pull the fill plug on a level surface and see if fluid leaks out or not, if it doesn't its low and isprobably leaking from the prop seals on each side of the diff. Get that checked out.
The fill plug is a square hole that you can use a 3/8 ratchet on i think....

 

With the car still, push on each rear corner. Do you hear the noise?

 

Does it make any difference if the car is under load? Heavy accel vs. light accel off the stop?