Brake noise has been a problem since the early days of motoring, and a lot of studies have been made, - from the energy source of brake squeal [ 1… 3] to the vibration modes in squealing [ 4…5] to the geometric coupling characteristic [ 6… 10]. These were discussed mostly based on bending vibration of brake components. However, a new cause of the noise was found in the longitudinal vibration of the disc rotor. According to our investigation, the occurrence of the noise has been increasing in the market. Fundamental studies and experiments were conducted. The existence of the longitudinal vibration noise was confirmed, and effective preventive measures were demonstrated.