Knee ringing when squatting common causes are the following: 1, the most common is the knee joint ringing, especially the most common in adolescents, mainly due to the squatting joint capsule and the surrounding cartilage friction extrusion, and cause joint ringing; 2, patellar slippage: due to congenital patellar insufficiency, resulting in the patella is relatively small, when squatting patella to the side dislocation, called patellar slippage, can also cause the knee joint ringing 3, intra-articular free body: due to free body in the knee joint activities, and the surrounding cartilage tissue and meniscus friction extrusion, causing knee ringing, sometimes accompanied by pain; 4, ligament injury: cruciate ligament injury can also cause knee ringing, this situation is mostly related to the history of trauma, pain is more intense swelling, and even can not walk, feel the joint instability; 5, intra-articular cartilage friction, causing patellar Femoral joint degeneration, meniscal injury resulting in popping and pain. If the knee joint is physiologically rattling, if there are no painful symptoms, it can be left alone. If the knee is rattling and painful, it is recommended to go to the hospital in time for examination and consultation, sometimes requiring arthroscopic intervention and interventional treatment.