It is not warped rotors. True rotor warp is very rare. If it was warped rotors you'd get the pulsation all the time at all speeds.
It's hardened pad material stuck to the rotors. And yes it's caused from heat. Moreover it's caused from improper bedding of the pads, or lack of, after installation. Especially with ceramic pads. After it happens pull over and look at the rotors. You'll see little comet like deposits. It's more prevalent with ceramic pads but can happen with any type of pad. Thickness of pads is not an indicator that this will or will not happen.
I'd put new pads on before doing anything else. And readjusting the BC would not hurt either.
