Clicking Noise when turning

OK, I've been having this problem for a little bit now.

The sound I am experiencing is the same kind of sound you would normally hear while making a turn on pavement in part-time 4wd....however, I am also getting the sound now when I am in full-time 4wd or even 2wd?

When in 2wd for a while it will eventually stop making that sound on turns, however, if I put it back into full-time 4wd, it starts right up again, and will make the sound again when I go back into 2wd.

Sometimes, it seems as though it might be stuck in Part-time 4wd, but I am not 100% sure on that?

Anyone have any ideas or suggestions on what this problem could be, or where I can start to figure it out?

Thanks!

Have you checked the u-joints in the front axle?

i did check the u-joints a few days ago, and the seemed OK. i really think the sound is coming from the TC, though.