Knee rustling sound is related to physiological popping, synovial fold hyperplasia, osteoarthritis, meniscus injury and other factors. 1. Physiological popping: it is a normal phenomenon, which is mainly caused by the negative pressure in the joint cavity and can occur in teenagers and people who usually do a lot of sports. 2. Synovial fold hyperplasia: patients with chronic synovitis and rheumatoid arthritis may have synovial hyperplasia, which may cause friction between the bones of the knee. 3. Osteoarthritis: Trauma, inflammation, chronic and repeated cumulative strain, congenital diseases or joint instability can lead to osteoarthritis of the knee. Clinical manifestations are stiffness, pain, tenderness, friction, swelling, deformation and limitation of activities. 4. Meniscus injury: mainly caused by sports and degenerative injuries, will be accompanied by joint popping sound. Rubbing sound of the knee may also be caused by the mismatch between the patella and the femur, when the knee appears to rustle the friction sound, it is recommended to consult a doctor in time, under the guidance of the doctor to confirm the diagnosis and treatment.