Either bent or bad bearings. Anythings possible and if there was a defect in it it could happen more easily.
I can't recall any specific cases of this happening, but that doesn't mean a whole lot. Used transfer cases aren't such a big hit dollar-wise and they're not that hard to install. Worst case you're looking at less than $400 to do it. Often you can get a JY case for $250 or less.