Rattling of the knee joint during activity is a relatively common occurrence, also called knee popping. There are two types of knee rattles: physiological and pathological. Physiological ringing is normal and not caused by disease. It is mainly caused by friction between the synovial membrane or ligaments and cartilage when the knee joint is moving, and can also be caused by sudden changes in pressure within the joint. Physiological ringing is not harmful to the joint, and the ringing cannot be repeated for a short period of time, while the ringing is comfortable. Pathological ringing can have various causes, such as osteoarthritis, meniscal damage, meniscal deformity, and intra-articular free bodies. Meniscal damage, mainly caused by trauma, can also occur with prolonged knee activity. The main manifestations of this condition are knee pain and a rattling sound when the knee is moved. The meniscus is a soft cushion between the knee surfaces that acts as a cushion, and damage to this tissue can cause pain and ringing due to physical frictional stimulation. Bone spur formation is a pathological condition caused by bone growth after damage to the cartilage surface of the knee joint. Due to prolonged weight-bearing activities in the knee joint, the bone spurs may become dislodged due to grinding forces and form free bodies inside the joint. These free bodies produce joint rattling when the knee joint rubs against each other, and may also be associated with some pain and discomfort. Most knee popping is normal, but most knee popping with other symptoms is pathological, so the patient needs to be diagnosed and treated in a hospital.