air condistioner in car

It is usually one of two things, first if the refrigerate is low and some of the oil and escaped, then the compressor is the actually problem, Usually, by adding a small amount of oil with take care of this. Second, the bearing on the clutch is dry and is about to freeze up on you.

Does the "pulley" make the noise with the a/c on or off or both? It it is both then 2 is the answer if only while the a/c is running then 1 is the problem.