I have a whine in my driveline. It is only when power is applied, coasting its quiet. I have:

9" Moser rear
custom built 3.5" driveshaft
Raptor 700R4 (did the same thing with old trans)
Spohn Torque arm & crossmember

I have done:
pulled 3rd member & rechecked gear pattern on ring & pinion
checked driveline angles +2 deg diff. @ trans & -2 degs diff. @ rear
Replaced rear u-joint

I'm perplexed. Any ideas ?

Maybe it's an axle bearing ?

Wouldn't a wheel bearing make noise anytime the wheel was turning, not only under power ?