115 horsepower Yamaha outboard loses power, develops electical noise?

Today, my Yamaha 115 horsepower two-stroke outboard developed a squealing electrical noise in the throttle, and the engine lost power at the same time. At first, the noise would disappear when the boat went slow but come back when I accelerated. Eventually, the noise became constant and the engine bagan to run rough when I accelerated. Does anyone know what would cause this? Help!