There are two constant velocity joints (CV) one on either end of the 1/2 shaft I believe. These joints consist of caged balls that when they deteriorate can cause some weird noises and I've experience a lock-up situation on a GM econo box when the worn cage and balls started to bounce around inside the outer bell of the CV joint. The hardened steel balls and cage where smashed into barely recognizable pieces. You don't necessarily have to have the boot fail first and then the joint sometimes this kind of part was maybe not up to specs or had a defect and just suffers a premature failure. I would think that the lock-up situation can't be to good for the remainder of the drive train, and a new 1/2 shaft is probably much less than a new rear end. Good luck!