Every now and then, maybe once or twice a day, DS has a small coughing "fit" (best I can describe it).
ETA- by a fit I mean 5 or 6 coughs in a row. He doesn't seem to have trouble breathing.
It's a loud, dry, bark. It sounds awful. I don't know what is causing it, he's not sick, usually it's when he's been running around/ excited, but not always.

Any ideas what is causing it?

It's been going on for about 2 weeks. He seems fine otherwise.