well, mine started out a little noticeable, a couple days went by and i put it on the lift, and didn't see or feel anything wrong, i checked the d shafts, and they appeared and felt fine. a week or so goes by and it got louder, so i put it up and didn't see or feel anything again, so i unbolted the front d shaft and i could make it squeak and it did bind slightly.
you can remove the front shaft completely and drive it. you can do that to make sure thats your noise, if the noise stops when the shaft is out you konw for sure. don't drive without the rear d shaft though, they're different. unless you have sye and cv d shaft.
don't use 4 wd till its fixed. other than that its not imperative, it is not under any power. but i would fix it as soon as you can do it.
worst case is in 4 wd it binds up and throws a u joint, and d shaft spins around wherever it wants, saw one guy have is front d shaft whack a hole in his trans.