My dad has a 2006 Frontier 4.0 Automatic. He has a sort of whining noise that sounds like a supercharger. I looked at it and it really sounds like it is coming from the a/c compressor pulley. It does it reguardless of whether the compressor is on or not. Is it possible to replace the pulley on the compressor or will he have to replace the entire compressor? Is this a difficult job? Thanks for any advice.