The third setup was a brand new loaded differential yes. He checks everything. He's been setting up rear ends for over 25 years, and never had this kind of wear/noise/failure before. They are fine on the street and fairly quiet after his setup. A couple passes at the drag strip, and the...
Here's the answers to your questions directly from him John,
#1. The cause of the ring/pinion noise was from the front pinion bearing failure. Preload was gone.
#2. No fore/aft play, but no preload.
#3. Yes. The nut was staked and had not moved on all 3 of the failures.