Thanks for the comments.
The AC compressor was actually replaced this summer. I could live without AC (I’m in WI, so surviving the three weeks of summer temperatures isn’t a problem), but the clutch on the compressor was going, causing a noise when the serpentine belt went around it.
It turns out that the problem this time is my clutch. As I understand it, there is a bearing that has shifted and makes the noise when the clutch is engaged, hence the reason I hear the noise when idling (with foot on clutch to disengage gears).