Just got back from fourbien and notice while I'm in low range and goin don hill and over ruts it make like a clonking sound doesn't do it in high range..? Any help??
I wonder if the transfer chain has stretched any. It would be worth changing the oil in the transfer case and checking the old contents for metal fragments.
It's a bit of work to pull the thing out of the transfer case and replace it, there have been a few people here with transfer chain issues. Have a read in this thread, entire transfer cases could be had for around the $300 mark.
Make sure that's the problem first, of course! There have also been issues with drive shafts out of balance, uni joints getting a wobble on etc, but if it's only happening in low range my guess would be that as the chain gets some tension on it the "loose" side is slapping the outer case, then the tension is released as the vehicle moves about and then repeats.