popping in 4wd

My '93 just started making a popping noise in 4wd, it does it in high and low, forwards or backwards. It was fine the last time I took it out, I was checking it all out, greasing it and changed t-case fluid so I could take it back out this weekend and noticed it was making the noise. I couldn't get the cv joint to take any grease in the joints, could that have anything to do with it? Any ideas? It rained four days hear this week, and I was really looking forward to getting in the mud.

blown or going out the door u-joints pop when you turn in 4wheel.

(truck not running/moving) try grabbing your front axleshafts and turning them without the tire moving... if the u-joint clanks around then thats your problem

Blown axleshaft joints will pop all the time in 4wd, even going straight (at least mine did) and when turning in 2wd. Not expensive or hard to replace.

Is it a popping noise or does it fill like the front end slip a tooth every time the noise is make?

If so it could be the chain it the transfer case but more likely the shift fork for 4wd is warn to the point that is not fully engaging! How did the fluid look when you service the t-case.

If it is the front axle joint, drowned the joints with some good penetrating lube and see if it gos a way.......Yes? replace the u joint in the axle.
As Oizarod115 and Archdukeferdinand have suggested.

I've been under it all afternoon, checked front diff, axleshafts, drive shaft joints, they all appear to be good. I had someone get in with it in 4hi with their foot on the brake in gear and step on the gas while I was laying under it. It is coming from inside the t-case, the drive line jumps when it makes the pop, pretty much come to the conclusion that it's the chain jumping in the case. It drives fine in 2 wheel, only trouble is in 4 wheel. I guess it's time to order some parts and tear into the t-case. The fluid in it was black when I changed it yesterday, it had only been in there maybe 2,000 miles, about two months, if that long.