[/quote] Not my area so a BTT for ya but more info, I was wondering if it was bad & you did the greasing/endplay to try & correct it? when did it start? any parts changes preceding this? [/quote]

The story is that I bought a 1970 Fury with bad rust for a parts car. I did drive it, but not at very high speed. I didn't notice problems with the 3.23 8.75 sure grip axle. My 1970 Fury convertible had an 8.25, 2.71 gear, open. I cleaned and painted the 8.75 rear from the parts car. I installed the rear in the convertible as prep for a big block conversion, which I have not yet begun. The axle shafts had a tapered roller bearing on one side and a non-adjustable bearing on the other, which was a mismatch. I had a tapered roller bearing installed on the side with the repair bearing, greased both sides, and set up the end play after I had installed the axle on the car. The noise appeared immediately with the replacement axle. I removed the pinion shaft nut and tightened to factory spec. I drove the car again and the noise remains.