Are you sure it's your ac, the PS pumps whine alot. If it only whines when the clutch engages then it is the ac, if it whines all the time it might not be. Be very careful with this, take a long handled screw driver and with the engine running plant the pointy end at different points and put the blunt end up near your ear, it will act as a stetiscope [or however you spell it] and help to locate any vibes. Just watch the moving parts or you might end up with a screwdriver permanently embedded in your head.