I've had this happen to me for years. At first it freaked me out. I had no pain, just the popping in the sternum when I would do dips or ncline bench. It eventually went away, but after a few lay-offs from lifting, it would always come back. A doc told told me it is very normal, that its an over-abudance of cartilage in the sterum that separates. He said some people have, some don't, and to not worry about it as long as it wasn't painfull.
Hey guys - just noticed this thread. If you dont have any pain with the sternum popping, then I would say to ease off the exercise that brings it on for a while and not to worry to much. If you have ANY pain in the sternum area, then STOP. I am in the final stages of recovering from what turned out to be an injured chest tendon. Talk about an injury that SUCKS. I tried to work around it, and I just ended up with symptoms of overtraining. My rotator cuffs went out (starting popping/clicking like crazy), my knees started to hurt. I felt like **** in general for over a month. I havent benched any real weight in over 3 months. I havent even trained chest at all for more than 2. The healing process for a tendon injury is long and annoying to say the least!
Im going to update that old thread of mine...so follow up there if you're interested.