1993 Tranfer Case Noise?

[flatlandcycle]

I test drove a 1993 1500 4x4, v6, auto 127,000 miles, today. Looking at the truck for my son's first ride. Anyway, the truck is clean and runs great until you slip it into 4x4 high. The truck makes this loud deep noise like the transfer case...? It sounds like a vibration, like a bad clutch but it is an auto. the truck moves and hte noise kind of comes and goes...

 

I put it back in 2wd and drove it back to the lady selling it. The truck runs great in 2wd... Any idea what would make that noise?

 

Thanks,

 

Steve