Rear end noise ?

Its hard for the uneducated/unexperienced eye to look @ a used ring & pinion to tell if its going to be noisy or not. A careful study of the teeth & some gear paint may give a clue bit its still hard to tell. most will howl around 38-47 mph ir seems. 1st set of 3.23's i took a hance on,sure enough wine @ 40 on light accel. Next set i learned from it the 1st one. & are quite. first set i even replaced all the bearings & set b/l to what it was before i installed new bearing's.