question: just like when you crack your knuckles or back or whatever.Been going on for a couple of days. Leaned back in a chair and felt a crack or pop in my sternum. It felt good and I ve felt the need to do it again whenever I feel a bit of tightness in my sternum. Now I can just do it by spreading arms and expanding the chest cavity. Is this normal? I lift weight 4 day a week. upper body on Mondays and Wednesdays