The classic squeal on startup or in the rain. The belt or its tensioner.
A glazed or worn serpentine belt, a weak tensioner, or a misaligned pulley.
A belt and tensioner job is cheap insurance. A thrown belt takes the water pump with it.
Reading about sounds only goes so far. The tuner on our home page listens in your browser and tells you what it hears. The app goes further: it names the exact fault, checks it against your vehicle, and tells you how urgent it is.