Firestrike87:
Yes, it can be intermittent but, eventually, the bearing will squeak constantly. Before you fork out for a new alternator, confirm the location of the squeak by holding a piece of tubing up to your ear and moving the other end around (tensioner, water pump, p/s pump, A/C clutch, alternator). The noise will increase a lot when you find the real squeak (could be the alternator, for sure).
Chris