Rattling sound when pressed under the left rib cage may be due to costal cartilage inflammation, intercostal myofasciitis, bone fracture and so on. 1. Inflammation of the costal cartilage: it may be related to viral infection, chronic strain of the ligaments of the thoracic rib joints, or nutritional disorders of the costal cartilage caused by endocrine abnormality, which may lead to rattling of the left side of the ribs when pressed with the hand, accompanied by pain. The pain will be aggravated when coughing or deep breathing, or during activities. 2. Intercostal myofasciitis: it is mostly caused by cumulative strain or acute injury, and may also be caused by cold, dampness or rheumatism and inflammatory lesions of fibrous tissue, which may lead to rattling sound when pressed under the left side of the rib cage, accompanied by radiating pain in the lumbar region and back. 3. Rib fracture: If the patient’s left rib cage is impacted, rib fracture may occur. Therefore, if the fracture site is active and the site rubs against it when pressure is applied to the site, a rattling sound may be heard. There may be other reasons for the rattling sound when pressing on the left side of the lower ribs, so it is recommended to consult a doctor in time to clarify the specific cause and carry out appropriate treatment if necessary.