Need to trouble shoot rear axle (GM 14 bolt)

[Old Rust Bucket]

Okay it's a 14 bolt 10.25 ring gear in a '76 C20. This problem started a few days after the truck was loaded over capacity. Started out as an occasional rattle and got progressively worse til it would rattle consantly between 30MPH and 50MPH. Then it started making a grinding noise. Got home and checked it, the diff. case was hot enough to fry an egg. I pulled the cover off and the ring and pinnion gears are fine, no shavings in the gear oil. (which was plenty full) No chips on either gear. I went on a hunch and pulled the rear driver's side wheel off. Pulled the axle out. Not sure what I was trying to prove, but when I spun the brake drum just right it would make a a very slight rattle. I'm confused right about now. If it was in the brake drum that does not expalin the diff. case getting hot. unless the oil is moving back and forth transfering the heat. I still wonder if there's a bearing in the diff going out.

Thanks in advance for any help.

Old Rusty Bucket