This only happens to me if I am sprinting outside and its windy with a high pollen count. My throat starts to get itchy and mucus starts to develop. But I continue on and it eventually goes away. I have seasonal allergies and whether I am sprinting or walking it will happen regardless because of the large amount of pollen in my neighborhood. It always goes away after the first couple of sprints and I have been running/hill sprinting for over 10 years. This happens to my friends and my fiance as well when they run with me and they have no known allergies like I do. It is basically all the dust and pollen in the air getting trapped in the little hairs of your nose and throat causing a slight immune response because your body thinks there is a foreign object about to enter. It is completely normal.
You may notice it more with vigorous exercise because you are sucking more air than when you are walking. A good tip is to try to breath through your nose more (even though its hard when sprinting). Your nose has a lot more hairs that really will defend your air passage from dust/pollen. Post workout use a neti-pot to irrigate and cleanse your sinuses.
"If man made it, don't eat it" - Jack Lallane
People say I am on a "crazy" diet. What is so crazy about eating veggies, fruits, seafood and organ meats? Just because I don't eat whole wheat and processed food doesn't make my diet "crazy". Maybe everyone else with a SAD are the "crazy" ones for putting that junk in their system.