I say replace belt, tensioner, maybe idler pulley, check vibration damper for strange movement, and finally check for coolant leaks. My belt has been squeaking high-pitched on cold start-ups, and it whines for the first 10-15 minutes of driving at any rpm. Had the belt and tensioner replaced a couple weeks ago, and maybe 75 miles later the squeaking came back. I think the vibration damper is causing my problem because it's rusted and doesn't look like it's moving the way it's supposed to. Just check everything before buying parts, but to be safe, I'd replace the whole pulley system since parts are cheap and getting rid of the whining is priceless.
