Owing to many excellent previous studies brake noises have been improved steadly, yet it is not easy to get effective remedies for improving the noises of dram brake.The authores took experimental analysis to find the cause of the noise of 650-670Hz on medium class trucks and buses. They found out that the main sourse of the noise is the backplate vibration caused by vibration coupling of 2 vibration systems, namely drum-shoe system and backplate system. This coupling was faded and dissolved by separating the resonance frequency of either system from another. This method was effective to prevent the brake noise. They conclude that the brake noise is caused mainly by vibration coupling.