whining rear

So for my 8.75 in my '75 Scamp, I purchased a used 741 open case with 3.55's. I replaced the pinion seal, the gears looked good, I measured the backlash and came up with .010" (not bad for used gears).

After installation, the rear whines. :banghead:
Not a howl and no grinding sounds, just a high pitch whine.
At highway speeds it stops when coasting and when I apply the gas pedal it starts. This is behind a 225/904 currently, with plans for a 383/727 in the near future.

Someone suggested that this was a pinion bearing noise. Any other thoughts? Is this carrier going to scatter? I was going to drive this to Carlisle this summer 180 miles from Pittsburgh. Now I'm not so sure.

Any input is appreciated.