could also be the transfer case. it is unlikely that your bearings would go before your synchros, but it can happen (if for example was driven with low level oil in it). Could also be worn gears, but again not likely. you could try and listen with a mechanic's stethoscope with the Jeep lifted and someone shifting gears and see where the noise comes from (t-case or tranny). You could also try to put the t-case in neutral and clutch pushed in while rolling (downhill preferably) - if it still makes the noise it is probably the output shaft bearing on the t-case (could also be the rear axle though, but probably you could tell that is coming from the back in that case), if it doesn't then it's either the tranny or the t-case input shaft.