Noisy rearend 69 barracuda 318 car

Rebuilt my first rear end in about 1982. This was 7.25 under a 67 slant 6 B'cuda with 86K miles on it. I had already done tune up with reman'd distributor, carb rebuild, valve adjust, etc... It ran great.
Whats next?... The rear whined like a horn blowing under load from about 40 mph up. Coasted fairly quiet. The gears did show some wear but new everything and smear pattern quietened it for the following 8 years it was our daily driver.
I put a 318 and 727 in front of it about 1986 after the slant poked the #5 rod through the block at 112K. The sad part is I put late model disc brakes and 4 LBP rallyes under it at the same time. With money spent on that 7.25 I had pretty much obligated myself to running a pair of bolt pattern adapters. Lesson learned. I wouldn't spend coins on one those rears again unless my options were as limited again. My current 67 273 B'cuda still has all its OEM running gear at 93K miles. This rear is quiet as one could wish for. Go figure. Good luck with yours