I just installed a perm lock in the front axle. I checked everything out with the Jeep up on 4 stands. Seems to work. I went off the pavement and engaged the 4x4 and I started to hear a poping sound from the front end. It really pops when I turn. Put it back in 2wd and no poping. Back in 4wd an poping starts up again. I think it is the axle u-joints, but wouldnl;t I hear it in 2wd. I checked the u-joints on the front shaft and they seem to be ok. the ring gear and pinon looked good when I changed the oil in the diff. The axle shafts where they meet together looked ok, the shift fork looked ok, I t just does it in 4wd not 2wd. Now when you perm lock the axle shafts the front drive shaft spins when the transfer case is in 2wd and both tires will spin. this is normal what I have been told. Any help would be nice.