Isuzu Repair: Isuzu Trooper intermittent grinding noise, automatic locking hubs, dry pavement

Question
After purchasing a '91 Isuzu Trooper w/2.8 ltr & auto transmission, it started making a grinding/growling noise. I found out that I had driven it 35 miles in 4H at speeds up to 55 mph! (I have never had a 4WD, & the seller said he didn't remember how to shift it...the label on the shifter was missing.  He also played around with the 4WD to show me that it worked--at least the 4L light lit up--but he didn't know not to shift to 4WD on dry pavement! If I knew better, I wouldn't have bought a 4WD from someone who didn't know how to use it!)  The noise starts after it warms up a bit, is intermittent, increasing the longer I drive, and only occurs upon acceleration--it stops as soon as I step off the gas. It sounds like it's coming from the transfer case--or rear differential? On one 6 mile trip, the noise was almost continual--then I backed it 50+' into a driveway; after that it only made the growling/grinding noise twice on the return trip. It has automatic locking hubs. The transmission works great (even after the seller overfilled it & told me it was OK)--I changed the filter/fluid and it wasn't burnt and there were no fragments, etc in the pan. I'm driving it very little until I can find out what's wrong...can you help me--at least give me some ideas where to look??!! I can't afford a professional repair, so I'm learning about 4WD systems to try and do it myself.

Answer
Well Carrie, using 4wd on dry level pavement doing over 35 mph is a good way to ruin your transfer case, and might ruin your tranny, although I would check your whell bearings/front and back, also check your transmission yoke, this might be the culprit, let me know how this goes ok?