For the case of ringing when you curl your legs, there are three main reasons to consider: First, there are individual differences, individuals have loose ligaments around the joints, resulting in poor stability of the joints, and when the joints are moving, there will be ringing due to the wrong movement, which is physiological and does not require treatment. Second, there may be free bodies in the joints, commonly known as joint rats, which can be stuck on the joint surface during repeated joint movements and produce a popping sound. If this happens, the free body needs to be removed under arthroscopy, otherwise it can lead to osteoarthritis over time. Third, there is a tear of the meniscus, after the meniscus tear can also be stuck between the joint surface, resulting in a popping sound, which can also lead to osteoarthritis, and requires arthroscopic surgery.