A/C Screaming at me
 

Hi,

I'm trying to get the A/C back up and running, and i'm glad to say it's 'working', but just about every time i use it now it screams (like a very loud screaching/grinding sound) from under the hood. It's definately to do with the A/C system, as it's directly controlled by the a/c button on the dash as well as the speed of the engine (compressor clutch?). If so, where can I go to get replacement parts? Rockauto (which has so far done well for me) has nothing, and almost everywhere else wants to only sell me the whole compressor.

Any help is appreciated. Thanks guys.