On a chain transfer case does the chain turn in 2 wheel drive?

does the chain in the NP 231 turn all the time or only in 4 wheel drive? i think i might have a loose chain, when i pop the clutch i get a clunk around that area.

 

it turns all the time... i just had a battle where my 4wd would cluck and make god awful sounds when i got on it ... pulled the drain plug checked how loos the chain was ... needlees to say i could move it an inch with my finger.... so if you wanted to check the chain you could do it that way should be had to move or not move at all with just your finger

 

yeah thats what my truck is doing. It makes a loud clunk. I can rotate the front drivshaft WAY to much. How hard is it to replace the chain?