Rattling in the knee is not due to a calcium deficiency. There are several possible causes for the knee to rattle during exercise. The first is a physiological cause, such as a rattling sound caused by a tendon scraping the bone surface during flexion and extension activities, or a popping sound caused by a sudden change in the position of the meniscus. However, this is not a sign of a disease, but a normal physiological phenomenon. The second type of knee rattling is due to pathological causes: 1. The majority of them are due to meniscus damage in the knee joint, which can lead to a significant rattling during flexion and extension activities of the joint; 2. Due to degenerative changes in the knee joint, proliferating bone spurs can lead to a rattling in the knee during movement. However, neither of these two causes is due to calcium deficiency.