My 99 TJ has been a daily driver with occasional light offroad to my fishing locations. I hardly ever use 4WD, but recently tried it. It entered 4WD and began making a terrible noise. It sounded like gears jumping over each other or chain jumping over a sprocket noise. The sound appeared to be coming from the transfer case area. Removal from 4WD stops the noise. It's consistent and repeatable. When it warm enough to try your suggestions, what steps would be best to locate source of the noise. I've driven the jeep a lot and it has over 105k miles. Thanks for any input.