all I can come up with is this,
I see no rubbing on the inside of the case. I am thinking that the bearing on the back side of the gear diff(the side without the screws) is binding on the diff when you tighten it. the bearings when pulled out and slid onto the output shafts, one side(with the bolts) leaves a small tiny gap between the cases that I can get a small knife blade in there to pop it off, the other side is tight up against the diff and is a pain to try to get off, thinking the outer race of the bearing might be binding with the diff.