I'm not sure, but it sounds kind of like a rib may be torqued from a subluxation. I get the same type of feeling sometimes and usually it gets better if I stretch both my elbows backwards often, and level with the height of my chest and try to make my shoulder blades touch as a reference point. They don't touch, the goal is to just imagine your inner shoulder blades trying to touch, while in a slow rowing backward type motion. I hope that makes sense. Sometimes I even hear it pop back in. I have had to see the chiropractor on more than one occasion to have it adjusted though. I hope it goes away soon.