I have a 2000 Saturn SL1 with 179,000 miles on it. For the past week, whenever I stop at a light and the engine is idling, I hear a rhythmic chirping sound. It's not very loud. When I am driving, I can't hear it. Sometimes when I idle, I have to strain to hear it, but sometimes it is quite clear. Could this be related to the serpentine belt?

With that kind of mileage, it could be a number of things. You have idler pulleys with bearings inside of them that do eventually dry-up and squeak/squeal. Belts can squeal sometimes if too glazed from years of use. Water pumps even squeak/squeal when worn.

I suggest that if you're capable, you loosen the belt, then turn each pulley in it's normal direction, spin them, wiggle them and see if any are too hard to turn, too loose, including the pumps/alternator.

Check the belt for cracks while loose and decide if it's time to invest in a new one based upon your up close observation.

NAPA tends to have just the bearings, if you're the type to replace/rebuild, dealers and auto parts stores have the idler pulleys with the bearings if needed.

good luck