transfer case noise / chain skipping?

[PyroMANIAC]

Dear experts!!!
I got a rb30 patrol here with grinding/vibrating noise coming from under the floor and sort of shudders the vehicle when in four wheel drive (Hubs locked or unlocked still makes noise in H4 and L4) when its under load but does not do it when i put it back in 2 wheel drive both diffs are fine and have been checked and also wheel bearings are fine and have been checked has 4" lift kit fitted to the vehicle..... my guess is the transfer case is shagged (but if this is the case what cases it and what's the best way to fix it?) and also another ideas of what it might be cheers