Over the last week I have noticed an occasional harmonic squeal when the clutch engages on the compressor. It sounds like a failing bearing and only lasts 2-3 seconds at most. My indy says the compressor is likely on its way out. It doesn't happen consistently and is very short in duration. How difficult is it to replace the compressor? If it is a bearing, how difficult would it be to rebuild the compressor? Or is something else likely the culprit?