On wet grass, any slick you could here a clunk. Problem with the electronic shift transfer case is that it waits for movement of the drive line till it engages. When there is moving gears it engages easier. with the toqure of the duramax it will spin the wheels when slick and that causes backlash, that goes clunk. I've had it in slick areas a lot. Sometimes I stick her in neutral and shift to 4h or back to 2h. I can hear mine disengaging also. They bind up. I hope I explained good enough, been awake a long time. Not saying I like it, get it checked out. But don't loose sleep over it. Apply brake in slick areas, let of slow, easy on skinny pedal till you know it's engaged.
