This is an indication that either your front or rear brake rotors have warped. Warping can happen as a result of driving hot brakes through cold water puddles (like warping a pan by taking it directly from your stove and putting it in the sink under your tap). Also, some rotors develop high spots on them as they age and one section of the rotor wears away faster than another. These high spots are felt all the way through the brake system. In either case, replacement of these rotors in the new standard of care.