Getsome

Hello everyone, hoping someone can shed some light on a problem I am having with my truck. It is a 2003 2500hd 6.0l which I picked up a couple of months ago. Now that the snow is finally here, I have been using my 4wd but have been having some weird issues. When I accelerate in any sort of quick fashion (not necessarily hard), or when I am turning, I get a loud and violent clunking noise and feel from my front end. This doesnt happen all the time, nor does it happen in 2wd. Sometimes it clunks on the passenger side, other times I can feel it under my feet on the drivers side. The previous owner said he had to have the transfer case rebuilt last winter because it went out on him, I am hoping my transfer case isnt shot. I have been told that it could be the u-joints? Others have said that its just the gears locking/unlocking?

I am a newbie to the 4x4 world as I have only owned cars up until this truck. Any help/ideas would be appreciated.