The title explains it pretty much! When I am rolling, there is a very loud rattle from underneath the truck, I think it is the transfer case but I can't be for sure. The problem is that I can't tell because it has to be moving at around 15-20 Mph or more to hear it. It sounds like something loose in the case however. The 4X4 works perfectly in Hi and Lo so I don't know what it would be.
Does anyone know of something like this and how hard would it be to remove the transfer case and open it to see what it might be.
I don't think it is the transmission or it would be rattling even at idle right?

Just maybe you have the same issues as I just posted

http://www.automotiveforums.com/vbulletin/showthread.php?t=956764