initial acceleration crackling noise from transfer case.

97 YUKON 4X4

I know its the transfer case because I put it in 4-hi, and the noise went away. In 2 wheel drive it sounds like crap.

The performance of the truck is the same as it ever was, just making noise and obviously doing some damage.

Is this major? Do I need a whole new transfer case or is this something that a local mechanic can fix on the spot?

Thanks for any help