My Car Also Goes "ping"

91 TSi AWD

When I drive in reverse and start to take off in 1st there is a loud ping or pink like sound from the rear end of the car. I will be getting under the car tonight to look into it further. I was just wondering if any of you have run into this before. I still have the stock 3 bolt w/original axles, it has 160k on it.

Any thoughts?

Thanks

Mike Ert