Does it do it in both 4wd and 2wd? Only when wheels turned full lock or straight on?
I think it sounds like a bearing if it does it all the time regardless. I replaced the bearings once on my Camaro, and left the castle nut too loose, for fear of overtorqing the bearings. Lets just say I was taking it all apart again a few months later and replacing bearings again because I left it TOO loose! Lesson learned!