Does he have a cold? Snot in his nose might be draining into his throat making him trying to clear it to comfort the uncomfortable sensation, and it might be hard to breath in that case. If you notice drainage in the nose give him some over the counter medicine. If it doesn't clear up bring him to the doctor.
It could be any number of things, the most likely being post-nasal drip due to sinus infection, a cold, virus, allergies etc... Trying giving him an antihistamine and see if that helps. Or an age-appropriate child's cold medicine.
The air could be dry and irritating this throat. Try having him suck on children's throat lozenges, or drink something when it happens.
However, if it doesn't appear likely that it's any of these, and reasonable measures such as those above do not help, then it's time to talk to your doctor. It could be any number of things from a tic (not necessarily Tourette's, many children develop transient tics that do not turn into Tourette's) to a problem with his thyroid.