Knee activity with friction sounds is often caused by the following: a. There may be peripatellar cartilage damage. This condition is seen in the presence of patellofemoral arthritis, or the presence of patellar tenderness. This type of disease involves strenuous activity of the knee joint, resulting in damage to the articular cartilage of the patella and femur relative to the joint surface, resulting in unfavorable activity and noise when the joint is moving. Second, there may be synovitis of the knee joint. This type of disease is due to cold in the knee joint, or in the process of rheumatism, rheumatoid arthritis, synovial membrane has a substantial growth, and then lead to the knee joint in the activity, the patella around the sound of friction. Third, there may be a case of osteoarthritis of the knee joint. This type of disease is common in the elderly. The cause is the overuse of the knee joint, resulting in severe wear and tear inside the knee joint, which then produces a sound. Fourth, it may also be caused by the free body inside the knee joint. This type of disease is mainly due to damage inside the knee joint, some small debris, and then produce a “pearl” type of free body. This noise can occur when the knee joint is moving.