Whining noise?

[woody82]

I recently discovered the rear pinion yoke on my 72 rwd had been damaged sometime or another. So I ordered a replacement and while I had the driveshaft off I went ahead and changed the u joints.I do believe I lined the driveshafts back the way they were but not positive.I snugged the pinion nut down pretty good but didn't bear down on it to much.The truck has a TH 400 tranny in it not sure if that's what came in it or not it has been out because it is very clean and seems to slam in gear pretty hard.My question is why would I be getting a low speed whining noise that wasn't there before?