AC Compressor noise

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With the temperatures rising every day, I finally decided to recharge the A/C system, it was empty since last autumn when I changed two of the pipes. It works well, blows cold, but there is sort of a grinding noise coming from the compressor.
The sound is only there at idle speed or up to 1500 rpm. If I rev the engine higher, or disengage the compressor (pressing the ECON button) the noise stops. What could it be ? The compressor itself, the clutch, the serpentine belt (made the short belt mod a while back), a bearing ?
Any ideas ?

[Shazam]

I think clutch is the most common thing to go. If it were something on the serpentine belt, you would still be getting the grinding noise even if the A/C is off (pressing ECON).

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So what should I do ? Let it be until it finally gives in ?

[Shazam]

Hmmm... I was half right. I guess it is the bearing in the clutch. People say if you let it go, the bearing can freeze and you'll end up snapping your serpentine belt. Best to replace that bearing right away. I can't find a good thread on how to replace the it, but I've found that you should buy a kit with a new bearing already installed, as it's a bit tricky to get the bearing out without breaking anything.

I hate linking to this site, but I'm a bit unfamiliar with the problem...
Who here has replaced the a/c clutch bearing? - SaabCentral Forums

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These past few days I covered about 800 km, and the noise is almost gone. Let's hope it's going to stay that way.

[rpiereck]

That could mean you have ground your bearing to the point where it's almost smooth. Not necessarily a good thing. Grab one of those automotive stethoscopes (you can buy them at NAPA for less than $10) and listen around the a/c compressor where the bearing is, while the engine is running and the a/c on. You should be able to (actually, you will) hear it better with the stethoscope.