whining noise when accelerating - from where?

[cdub2010]

I have finally got my truck drivable after a year and a half of fixing a ton of stuff. Now im chasing down a whining noise when accelerating from 20 to 60 mph. The noise seems to get louder the faster I go. It goes away when I let off the gas. I havent gone over 60 yet, still in shakedown mode.

Background info is the truck is a 71 LWB 2wd 350/350 with 3.73 open diff. It has had a serpentine setup from a 90 chevy with new alternator, fan, fan clutch and waterpump. The drivetrain has new flexplate, rebuilt th350 with new converter, re-balanced drive shaft with new carrier bearing and new u-joints, the rear axle fluid changed. Rear gears were a bit rusty from sitting for so long, looks like a few teeth are lightly pitted but no chips or bigger damage.

any ideas?