Rattling in the shoulder may occur with the movement of the shoulder joint. For example, when the shoulder joint is moving in a certain range, or when the shoulder joint is moving vigorously in a wide range, thus appearing as a rattle. There are several common reasons for this: First, physiological popping. Because the shoulder joint is a relatively closed chamber, the pressure inside and outside the chamber changes drastically during strenuous activity or a wide range of activity, resulting in a pressure-releasing popping sound. Second, it is seen in frozen shoulder. The inflammation of the soft tissues around the shoulder causes the shoulder capsule, ligaments, tendons to become hypertrophic and heterotopic ossified, and so on. Third, it can be seen in shoulder arthritis, including degenerative osteoarthritis or traumatic arthritis caused by injury. This can lead to deformation and hyperplasia of the shoulder joint bones, which can cause the bones to rub against each other when the shoulder joint moves.