the big bang theory

not quite..
when i engage 4low.. crawling up hills i hear a bang noise. Thought it was the chain slipping on the xfercase but it doesnt make any noise on flat ground .
So last time out i was going up some rock terrain and every time it would come up on rock on driver side, i'd hear a bang.. the bang bang.. then bang a few seconds later.. but its not repetitive.. it just happens when i climb up hills..
Any ideas? is it the splines on the front yoke slipping? axle splines slipping?
front ujoint?

i dont know where to begin..
2wd it hauls ass.. no noises.. 4wd full time.. on the road no noises..
any ideas?

mark

It's not going to be splines slipping... if those were slipping you would have much bigger problems. I'd bet it's the chain slipping under extreme tension - try turning a tight circle on dirt with it in 4lo. If it's not that, check to see if your sway bar or sway bar links are poking into your leaf springs when the driver side flexes.