So I put my xj in 4wd other day and as I drove there was a clicking noise coming from under or front of jeep. It's not the engine and only does this when in 4hi and 4low. Any ideas what this might be? Or where I should start looking?

 

Failing u-joint making noise when you put power to it?

 

Yes but only when in 4 wheel drive so most likely front u joint?

 

That'd be my guess, probably one of the front driveshaft u-joints. If the noise changes when you turn right or left, could be the axle shaft u-joints.
Give each of them a twist and see if you feel any slop, check the bearing caps for rust dust, etc.

 

Alright cool thank you I will be check it out tomorow

 

Sound is coming from inside transfer case. I was told the chain is probably stretched. Hopefully that is all that's wrong with it