I eliminated a persistent squeal last week by scrubbing the rims -- this was after toeing in, sanding the pads, eliminating vibration. I must have run through something incredibly disgusting and sticky because it took a lot of elbow grease to get the crap off. Literally, I could feel where the pads would have been skipping as I cleaned it. I used Goo-Gone and steel wool. Bike stops on a dime now, no squeal.