Wannabetruckguy

My 1984 Toyota pickup is finally up and running but now I have another problem. It seems when I put it in 4 wheel drive, with or without the hubs locked, it make a rattling noise. Soon after the rattling noise turns into a grinding noise. I was told, by a friend, my drive-line need to be lubed so I took it into jiffy lube. They filled up my diffs and transfer case saying that my transfer case was near empty. As I leave I put it into 4 wheel drive and they noise is gone, for about 30 seconds. So I pull over take it out of 4 wheel drive and get home. When I get home my rear diff has steam coming off of it. It has recently snowed so it could be the snow dripping on it but it shouldn't be getting that hot, should it? Any ideas on where to start or what to do?

With a closer look it is the rear diff steaming not the transfer case.