97 ZJ possible alternator problem

I have a 97 ZJ with the Orvis package. 318 engine, 44RE, 249. It has

145.000. It has been meticulously maintained. Today on the way to work (44 miles one way) I started getting a gravelly rattling noise in the front. I have isolated the noise to the front top of the engine. The noise is louder at the alternator than at the ac. It sounds like rocks in a wheelbarrow being pushed over a cobblestone road. Voltage has not changed. battery is still getting over 13. Question: can it be rebuilt? and if so any recommendations. if it cannot be rebuilt, what would you recommend? My wife won't go near the jeep (a good thing?). I can do all of the work myself and have done all required work on the jeep myself including rebuilding the 249. Can you give me ideas? Thanks