It's the wear indicator on your brake pads. It's designed to start squealing before the pads are gone so you have time to replace them before the brakes fail. New brake pads will fix the problem.
This is a do-it-yourself job. It's not overly hard. Get the parts at NAPA, not at your dealership, to save money. Don't let them sell you carbon-kevlar pads like they always try to - - it's a Metro for chrissake, you don't need performance brakes
