Its a 91 f250 with automatic transmission manual transfercase and automatic hubs. I put it in 4wd tge other day to cross a field. Now its out of 4wd but sometimes i take off and I begin to hear a grinding noise. Sounds exactly like metal dragging on pavement. Then when I drop below 5-10mph I get a LOUD clunk that sounds like a brick got kicked up and hit the bbottom of the truck. Its hard to explain but its intermittent and usually only does it for the first drive aftersisitting for an hour then it doesn't do it anymore until I shut it off and let it sit for about an hour. I'm completely lost.