I have had some odd pain in my ribs every now and then. They don't feel like they are coming from inside the chest, so I don't worry about it being a heart attack.
It feels more like a cramp. I have a rather large chest and I suspect that the pains are caused by the muscles underneath the breast tissue when they get tired or if I'm wearing an ill fitting bra.
I find them very difficult to relax, but I find that if they are cramping up a fair amount that a tab of ibuprofen can help and a hot shower can do wonders also.