[legion]

Unless you can physically feel the brake pedal pulsating, it's usually not warping. Usually, it is simply oxidation built up on one part of the rotor but not another part. This can be caused by washing your car on the driveway (the calipers protect part of the rotor) or having the car parked in the rain.

This happens to my wife's car every single time it rains and she has it parked at work. The solution? Taking the car out into the country, winding it up to 70, and applying the brakes firmly until it comes to a complete stop. (Basically re-bedding the pads.) It wipes the oxidation right off of the rotors.