Heres some more detailed info.
Last time I was out wheeling a month ago, I heard a pop or clunk type of noise while climbing or pushing through a deep set of muddy ruts. I have heard it in 4Hi and 4Lo both. You could hear and feel it. I couldnt tell exactly where it was coming from but it sounded like the front axle or transfer case. It was only under heavy load, not just driving or smaller hills and muddy ruts. I chose to end my day of wheeling before it went completely. That was about 500 miles ago. This is my daily driver so this 500+ miles was city, to and from work. No noise since.
Since I planned on doing it soon anyway, I put in a SYE and CV shaft, thinking that if it was in the transfer case I would see something. Well the SYE and CV shaft went on fine, nothing unusual in the TC or with the old rear drive shaft. Also the magnet in the TC was pretty clean, no chunks and only a little of residue to wipe off.
I took it out again today to a local place that has a couple steep but low hills. I did this to see if it was better after the SYE and CV shaft and climbing a hill in 4Lo produced the sound again. Definitely coming from the front. To me it sounds like a stripped gear. I pulled up against a smaller hill in 4Hi and gave it some gas. The rear tires spun a little, the front didnt and I heard the noise again, now a persistent slipping, mild grind while in 4wd and trying to climb.
4Hi and 4Lo drive fine, no weird noise, only when I was trying to climb. Makes no difference if Im turning or going straight, no noise. Its only when in 4wd and Im trying to climb.
I will plan on pulling the cover tonight or in the morning if thats the only way to tell if the problem is in the axle.