I just broke 2 teeth of my pinion and I want to share what I heard, saw and did.
Okay car has 165,000 miles, 305 TPI/A4, Auburn(stock 88w2.73)
Here are my sympthoms that I had:
Inital:
I heard a rubbing sound that would alter in sync with application of the gas pedal. A tonk-tonk-tonk...faint in the beginning.
Next day:
The sound would increase but it was difficult to tell if the noise was from the tranny, driveshaft or rearend.

Next day: Noise incresed can plainly be heard and felt in the car.

At this time I'm still puzzled about the source of the noise.
Troubleshooting:
Raise rear on car on jack stands and put the vehicle in Drive/idle
1. Looked for rubbing on driveshaft,
2. Used a long pipe as a stetopsope and placed it on the tranny and rearend...rearend seemed to be the noisier one.
3. removed wheels and drums ..checked for problems
4. Removed rearend cover>> found 2 pinion teeth resting in the oil.
Sorry this is long, but maybe it will help someone in the future.
Currently car is in the shop getting 3.23