This happens most often when i am backing out of a parking space and turning at the same time. I start to press the gas and i hear/feel bad vibration that seems to be coming from somewhere within or behind the transmission. I checked the tranny mount and it is fine. I couldnt think of anything other than maybe its the differential? The car is a 96z28 A4. These cars have a limited slip differential right? I have a bad feeling this isnt going to be something i can fix on my own. Suggestions please.

 

I would start by draining the fluid,. clean all the crap out of the housing, then refill and add some GM limited slip additive. If that doesn't do it, then possibly your posi is going. Be sure to use only the GM additive.