373 Rear End Whining

No whining is normal at all with any gear set. None, zero, zilch. You'll see people make reference to "sometimes low gears whine, blah blah blah" that's bull crap. Properly set up gears don't make a sound. Brand doesn't matter. If they make noise, they've been improperly set up. Period, end of story, over and out, Roger wilco. In cases like yours where whine happens on accel or deccel, you can look to the pinion gear depth as the blame. Sometimes....sometimes.....SOMETIMES you get lucky and the pinion nut has backed off and you can retighten it and all will be well, but it's seldom. Since the pinion nut torque can affect gear depth, it's something to check, but don't hold your breath. There is a silver lining of "sorts". IF and I mean IF you catch it quick enough, you can correct the gear depth and the noise will vanish. But, once the gear pattern sets up, it's too late. Nothing you can do will stop it. Good luck. I hope you get it. But don't let any shop run some bull crap by you that "it's normal until the gears break in" or some other total ridiculous nonsense, because that's just a lie basically telling you they don't want to mess with it.