chirping noise when idling

Hi all -
Recently my 97 Legacy Outback has been making a chirping noise when the engine is idling. It seems to lessen or go away as the engine gets
completely warmed up. It also goes away when the car is actually moving. If I come to a stop at a light, the noise is present. Also, the noise seems to only be present if I step on the brake (or get louder with the brake). Furthermore, I've only really noticed this problem at night (haven't been out in my car much during the daylight lately). And, if I turn off the headlights, the noise goes away. So I'm thinking an alternator problem or a belt problem having to do with the alternator. Anyone have any ideas?
best, jon jlarosa at alumni dot brown dot edu
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Jon LaRosa wrote:

Aircon belt idler pulley. If you're good with tools, you can remove it, clean out the old grease and reinstall it. Otherwise, maybe a $100 job at a shop.

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