My '84 Toyota 4X4 pickup recently started making some thumping noises when backing up. After shifting into first and moving forward, I can then tell that the auto locking hubs have tried to lock (but I did not shift into 4WD). Is the thumping noise a sign that the hubs are shot?

Could be. There was a thread on Yotatech a few weeks ago where the truck would start to bind up going in reverse. Poster swapped in some manual hubs and the problem went away. Or pull the hubs off and see if they need cleaning and light lubrication.

So you saw that mess, huh.

That was me.

I was having a problem when I went from Reverse to forward. If I put it in 4wd for a few feet then back to 2wd the clunking noise would go away...
I found a bad auto hub on the passenger side. I had to put rotors on the truck (different problem, warped rotor), so I had to go in anyways...
I had a pair of manual hubs in the garage, so they went on, and the noise is gone.
The one auto hub was definitely bad. Not sure how they operate, but there is a large coil spring in there and it was stuck in the spindle when I removed the main hub body.. it was not this was on the drivers side...
Simple fix is to replace the autos with the manual hubs....Better part and better for mileage in the long run.....