An electrical whine that climbs with revs. Bearings or diodes inside the alternator.
Worn alternator bearings or failing diodes leaking noise into the electrical system.
Test charging voltage. A failing alternator strands you at the worst time. Weeks, not months.
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.