Especially for MamaToThree:
Aside from the condition mentioned - sometimes a much simpler problem occurs and that is that you can have a ribhead out of place - that popping sensation is often one of the indicators! This sometimes occurs from bouts of coughing, though of course there can be other reasons too, such as lifting kiRAB, or other heavy objects.
Find the spot that hurts at the chest & feel around that area - tracing it back around to the spine - feel around the spinal column and take note if the vertebrae seem to be out of line with those above & below the area that rib is connected too. Sometimes deep muscular tension is enough to pull bones out of alignment as well - so consider finding a good Osteopath or a Chiropractor to check your overall spinal function & have them check the ribcage as well. They can put a displaced rib back where it belongs. More than likely this will resolve the problem!
If the muscle tension seems to be the culprit (as to the cause) take a look at the stress levels in your life - as well as cutting back on caffiene & sugars as they can create more tension & pain in the body. Consider getting a good deep massage - not just relaxation
Swedish Style - every 2 to 3 weeks at first, then at least every 4 to 6 weeks. Add in other activities that will get you moving & stretching - such as yoga, tai-chi or possibly a gym where you can work with a personal trainer to help your body function more easily.