If the knee joint rattles during activity, but is not accompanied by joint pain or restricted activity, it is caused by physiological factors, mainly due to friction between cartilage and cartilage in the joint cavity when the knee joint is active. If there is localized pain and limited movement of the knee joint, pathological factors should be considered, such as long-term wear and tear of the articular cartilage in middle-aged and elderly patients, resulting in hyperplasia and a popping sound when the ligaments are pressed during activity. It may also be due to strenuous exercise, resulting in damage to the meniscus within the knee joint, or a congenital discoid meniscus that causes a popping sound. Laxity of the joint ligaments can also cause frequent snapping of the joint. Pathological rattling symptoms require prompt MRI of the knee joint to identify the cause and provide targeted treatment.