NP203 making noise? or something else

[Adams74Chevy]

I have noticed that on the few occasions I've had to drive my truck lately that it sounds like a clicking noise when it's in gear is coming from the transmission/transfer case area. It is steady clicking but faint compaired to my exhaust so it's a bit hard to hear. It does seem change in speed depending on rpms. Am I crazy in thinking it's something inside the transfer case it's a NP203 that was converted to part-time by a previous owner. Or could it be something in the transmission or the flywheel? I mainly hope I can either quickly and cheaply fix it or be able to put it off until the spring since they're saying this winter is going to dump a lot of snowaround here.