My evo is 60k miles and I just noticed that a bolt thats keeping the alternator assembly sandwiched together has completely backed out. It was just dangling there. after a lot of patience and trickery, i managed to bolt it back up. I tightened another 2 bolts that were also quite lose. You might want to check yours out!

 

i had that happen to me when i first bought my Evo. Left me stranded on the highway. once i bought a new one i removed the bolts and used locktite on em. never had a problem after that.