If the noise is more dead center then on the left or right then it sounds more like something with the transfer case itself.

How many miles are on the truck?
Does the "clicking" sound change speed as you driver faster?
Put the truck in 4HI and drive straight and slow (no turns on dry pavement)
Does the sound change at all?

This is one that can be be difficult to pinpoint without hearing the noise.

You could have either a bad universal joint or possibly one or more of the output bearings on your transfer case that are worn out. It depends on the noise and could be something else entirely.
Also be sure to check the fluid inside the transfer case itself. Low or very worn fluid can cause odd noises here. Also check the fluid for metal shavings as this could indicate a more serious problem then just worn bearings.

 

Damn pretty mutch hit the nail on the head. I brought it to a friends mechanic who knows his stuff. (He happens to have a 97 jimmy too) come to find out the transfer case has no oil, bone dry, (The one thing midas did not check cause there was a shield in the way with four bolts) Also for whatever reason the 4x4 is constantly trying to engage the front, however the front tires do not spin. Its not in 4wheel, but is still trying and the drive shaft is constantly spinning.(Hence the noise) And when 4wd is engaged as said before sounds serious, won't turn, the whole truck snaps to the way you turn, kinda scary.(Did this before I read the post, mechanic did too and said was not normal) So as of now I know I need a transfer case as it won't dissengage the drive shaft, and also probably a drive shaft too, . This will be a fun one.