Yep, probably just 'a thing' given the location. Indigestion/traped wind most likely. Could also be the different geometry of a road bike, does it happen when you are on the drop bars? But of coarse go see the quack. Perhaps suggest a Stress ECG/EKG and or a chest X-ray if it's worrying you. Even just the reassurance of the Doc can make these things go away. Don't go all paranoid, if you trust your Gp go with what they say.

Good health.