When I was checking out the '06 MCS today, I heard a pretty loud rattling sound which seemed to be coming from center of the front behind the radiator. Turned off the A/C and the noise went away completely. I thought the a/c compressor was further to the left but it about has to be the compressor making the noise. The a/c does work but didn't seem to get quite as cold as it should. Thoughts? Could it be the cooling fan itself?