96' 1500 Reverse pops out

[BobbyBobby]

Hello, I just bought an automatic, 4wd 1996 GMC 1500. It drives well and no problems except for when I sometimes put it in reverse. It will make a little clunk noise and then a spinning sound. I wait for the spinning to stop and then put it in park and then back in reverse and it works. What would be causing that and is it a DIY project? Thank you in advance for your time.