1998 Chevrolet Other

Hello, I was wondering if someone could help me out. I have a 1998 Chevy Prizm with 108K miles. I just noticed that when I am in park or at a red light my car makes a high pitchs whistle/whining sound. This only happens when in park or not going more than about 5 MPH. The noise is defintely under the hood, either the engine or maybe one of the belts. Any thoughts on what that can be? It just started today and I did not notice it in the morning.
July 25, 2006.

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