my alternator belt made a very annoying high pitched noise, so i took it to the shop and they tightened the alt pulley. but now, majority of the time, it makes the same noise on startup, but then stops after a couple seconds. is it just a wornout belt or could be it something else?

 

Did you tension the belt by using a prybar on the alternator then tightening the top bolt?

 

Take it back to the shop and tell them to fix it right, if its the alternator belt all you do is loosen the top nut, stick a pry bar in there and pull so it gets tight.