It sounds like the chain in your transfer case is slipping over the teeth driving it/the theeth it drives, causing the sound you describe.
The process of changing it is described in viewtopic.php?f=3&t=23765&p=179168&hilit=transfer+case+chain+pictures#p179168
Sigi
The process of changing it is described in viewtopic.php?f=3&t=23765&p=179168&hilit=transfer+case+chain+pictures#p179168
Sigi