I know when belts start to wear out (just from getting old) they can screech 'cause they are loose and starting to slip. I think you said you checked that, but maybe check again?
Also, since it was close to the alt., maybe it's the pulley? Like 05horse said, check all the pulleys for tightness.
Some other checks: make sure your belt is lined up. With the car running, make sure it stays in the same path and doesn't wiggle. Look for any cracks along the ribbed side: they indicate the belt needs replaced. Maybe have your alt. checked out by somebody who knows about them... good luck and let us know what ya find. The more specific info you give, the better answers ya get!

__________________
YELLOW JACKET = 1998 Chrome Yellow V6
POWER: BBK CAI, TB, UDPs; Bosch Platinum +4 plugs
BEAUTY: black projector headlights, taillights, and mesh grille; 5% tint; shorty antenna; interior billet
ROLLERS: XXR 006 black spoke with blue lip; 18x8.5 & 9.5; BFG KDW/2 245/40R18 & 275/35R18
DRIVER: Jonathan, 6'2, 190 lbs
RIDER: my wife, 5'4 brunette hottie

and my 1st baby on the way...
