A patient’s knee keeps ringing because the human knee joint is under negative pressure, consisting mainly of joint fluid and air bubbles. When the patient moves the knee joint, the pressure inside the knee joint gradually increases and the air bubbles gradually rupture, resulting in a ringing sound. This is a normal physiological phenomenon and does not require special treatment. In addition, if the cartilage, meniscus or synovial membrane in the knee joint is damaged or there is osteophyte growth, the joint space is narrowed and the knee joint is moved with friction and rattling, and the patient will have pain and swelling in the knee joint, which affects the knee joint movement. X-rays and MRI films of the knee joint can be taken to make a specific diagnosis.