could be a pulley bearing wearing out. Take off the AC belt and drive without it and see if the chirp goes away. If so, you know it's one of those.
You could try the same with the main belt -- but you won't have power steering (or power brakes?) and it will get real hot real quick... so i'm not recommending that.. (but i might do it in the driveway, ha).
You can check your pulleys pretty easy with the belts off. Just take the belts off and spin them -- particularly the idler or tensioner pulleys. they should have resistance and stop after a turn or 2. They should NOT spin freely. if they spin freely, the bearing on them them is shot.
I had to do do the same thing on my C5 Corvette -- had a couple idler/tensioner pulleys that went bad.