Did you ever figure out what this noise was? Mine has started making the same noise, or at least sounds very very very similar.
It's not the belts / pulleys / water pump. It seemed to start after a belt / pulley refresh, but we took the belts off and the noise was still there.
It seemed like maybe it was coming from the crank damper pulley, and placing a screwdriver just below this I could hear the noise very very faintly. I think the oil pump is around this area, but it really was faint, so I'm not sure....
It only seems to happen on warm idle. If the car's cold it sounds fine.
Oil was changed only about 2k miles a go, shortly after I got the car. Mobil1 0w40 New Life.