Synovial crease syndrome and knee meniscus injury are causes of knee ringing, as follows: First, synovial crease syndrome: mainly due to excessive synovial membrane hyperplasia in the knee joint, synovial crease is larger, when the knee joint activity 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, and most of the joint popping caused by meniscal injury will be accompanied by pain.