Sternum pain years after mitral valve surgery

I am a 53 year old male and had mitral valve repair at Cleveland Clinic in 2005.  I continue to experience low to moderate pain in the sternum area - especially when I take deep breaths or sleep on my side.  Sometimes the sternum will "click" if I press it in with moderate fingertip pressure.  I do work out with weights and have tried to avoid benchpressing or lat pulldowns which seemed to exacerbate the problem.  However, lately, even jogging and aerobic exercise seems to bring the pain on.  The pain is dull and broad, so I cannot discount the possibility that GERD or some sort of esophageal issue is involved.

This issue has been reported previously in the forum (RayW, Jul 04, 2006) but I was hoping more spefic advice might be available - e.g., What procedure might help me determine the cause of the pain?  Thank you.