35 Year Old Endurance Athlete In Seemingly Good Health. 5'8

35 year old endurance athlete in seemingly good health. 5'8 158lb (71kg). No history of prior conditions. Chest pain distal left clavicle about two inches subtle pain similar to muscle strain for months but increased significantly today. Shooting pain in chestwall upon inhale. No numbness, no tingling, no burning, no shortness of breath. The only other thing is a distinct popping sound seeming near sternum. Any ideas I'm a little scared.