Why is my pit bull swallowing hard and coughing but acting normal?

If he is like most young pitties I know, he is probably a maniac. Maybe he banged his throat on something or overdid himself when he was pulling / playing. I have three myself and they have a knack for throwing themselves into things very hard. If this isn't the case most likely, than there is potentially some inflammatory, infectious, or allergic process causing Gronk to act out of the norm. Since he is currently stable and not in any direct distress, you might consider scheduling him a regular veterinary visit. If matters do not change or improve by the time that visit rolls around, take him in for a check up. If they are improving or gone before than, cancel it. Obviously if matters are worsening or have reached a point that are unacceptable to you, you should have him seen on an emergency basis through your local ER clinic. Hope this makes sense.