[Keith Seymore]

When an axle does generate noise it is typical for it to whine on accel - or - coast - or - decel. But rarely more than one of those conditions. So your experience is typical in that regard.

It also occurs in a very specific range because the driveline forcing function is not that powerful compared to the mass of the vehicle, meaning it needs the multiplying effect of resonance in order to generate enough power to be a disturbance. Not like a tire problem, where usually once it starts it just keeps going as you increase speed.

It could be a result of an incorrect setup in terms of pinion depth or backlash. If it has been "broken in" in this configuration then it has likely taken a set and there may not be an option other than changing the ring and pinion to a new setup.

Driveshaft balance has nothing to do with it. Imbalance is a first order of rotation disturbance; gear whine is a function of the number of teeth on the pinion gear (41 divided by 11 = 3.73, or 11th order of rotation for you). Every time the pinion tooth hits the ring gear it creates a "kick" causing the drive shaft to resonate torsionally, and that's what you are hearing.

K