The causes of meniscus injury without pain but with popping include meniscus free, knee joint interlocking and so on. 1. Meniscus free: after meniscus injury, if not fully recovered, there may be part of the meniscus in the free state, when the femur and tibia movement, the free part of the meniscus may collide with the femoral condyles and tibial plateau and produce popping, such as knee flexion movement may occur popping symptoms. 2. Knee interlocking: If the knee joint suddenly locks or jams due to improper movement during exercise, then popping sound will occur during the process of returning to normal. If the above symptoms occur, it is recommended to go to the hospital to find out the cause of the disease and under the guidance of the doctor for regular treatment.