[Peter B - CV8]

Might be resin deposits on the rotors (from the pads). What's your braking style like ? ie when stopping heavily at the lights do you engage the handbrake - or just leave your foot on the brake pedal (in certain cases, this can create a hot spot & cause resin from the pad to stick to the rotor. Can also cause a hot spot on the rotor & lead to rotor distortion).