my rear wheels have an intermittent squeal, as though the brake pads are worn.

the noise could be caused by the condition of the rotors. if there is a rust ridge that his hitting the brake pads or machined surface is pitted with rust. also the pads could have brake material trapped in the groove of the pad that would need to be cleaned. have them serviced to make sure these conditions are not a problem and that the pads and caliper slides are moving freely.