Rattling/knocking sound when the compressor is engaged. Not to loud. Much louder for first couple of seconds after engaging. No change in engine RPM. It's quiet with the compressor turned off. Everything is working fine. I would like to be certain the compressor is really bad before tearing into it. If I remove the serpentine belt and turn the compressor by hand (with the clutch engaged) will that cinch it? Is there any possibility something else would only be noisy while the compressor is running?

From what I've read in old threads, I'm looking at a new compressor. Just hoping it could be something else.
Thanks, Dan

1999 C280

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2012 E350 Bluetech