There are two main reasons for the ringing sound when the knee joint squats: First, due to the patellofemoral joint instability of the knee joint, mainly due to congenital development or injury to the quadriceps muscle and patellar tendon position, it will lead to the patella and femur can not be completely attached, there is a relatively large friction on one side, when squatting with the flexion of the knee joint, it will lead to this position instability, gradually return to the normal position, this The two bones will rub and squeeze during the process, resulting in pain and a rattling sound. The patient’s knee will be unstable as it flexes and gradually returns to its normal position.