Take off the serpentine belt and see if you still get the noise - that will tell you if it's the alternator bearings. The fan bracket pulley bearing can and does fail, but it's difficult to determine which of those bearings is making noise.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum