The causes of knee ringing are synovial crease syndrome, knee meniscus injury, etc., as follows: First, synovial crease syndrome: mainly due to excessive proliferation of synovial membrane in the knee joint, synovial crease is larger, when the knee joint activities crease will slide over the femoral condyles, thus will occur popping, synovial crease caused by the knee joint popping generally does not cause pain; second, knee meniscus injury: in the meniscus When a tear occurs, the meniscus will curl up as the knee moves, sometimes causing an obstacle to joint movement and even joint compression and popping, most of the popping caused by meniscal injury will be accompanied by pain.