Its been awhile but as I remember from triage...
The most common is a broken rib. You can tell this by severe brusing and or direct pain on the point of impact.
So being that your a fit guy, start feeling along each rib, and you can generally find the spot in question, inflammation can be a good sign.
Your sternum can also make noises like that but that usually means a severe fracture and youd know it.
In any event, take it easy, really easy. Fractures ribs can sometimes splinter when you continue the same actions over and over (MMA?)
Ibuprofen and heat wraps for pain and to reduce swelling, not cold packs. The jury is probably still out as for cold vs heat.
The most iv ever seen is a chest wrap for multple fractures, otherwise there is little they will do. Luckily your rib cage holds itself together pretty well.
Hope that helps