I replaced my 9" rear with a unit built and supplied by Currie 3.73. It made a howling noise when in between accelerating and decelerating, kinda like coasting. I did put a heavier
oil in it and it helped a lot. Years later I went to a 3.50 ratio and the mechanic shop who specializes in rear ends used Richmond gears and said they Richmond used to be noisy but now they are quiet. I dont hear that howling anymore so assuming Currie sets up their center sections correctly, I believe some gear manufacturers make better quality or maybe tend to have a quieter mesh.
John