Thumping Sound 83 300TDT

Allright, let's see what we come up with. We drove from Florida up the Alaskan Highway in my 83 300TDT this summer, no problem other than an annoying metallic thumping problem from the rear driver side. When I checked the rear end the passenger side half shaft had leaked all the fluid so i replaced it on the road with an after market halfshaft, I actually replaced both sides for safety. On return trip back to Florida the sound began to reoccur. Everything I have seen published say either Wheel Bearings or Pinion Gear. The sound goes with the rotation of tire, is metallic, but is not always present. Could it be the U-Joint hitting the frame from an overloaded vehicle? Or is it the rear wheel bearing, which I shoul have replaced when I did the halfshaft. Or is it the U joint, which has no significant play in it. Ideas, comments?????