Some dogs do the humping as an outlet for excitement. They don't know how to direct that energy when they are happy or over stimulated. My advice would be to get him to exercise more. Maybe take him for walks or play fetch in the yard with him or inside. If he uses up that excitement on other things he may stop the humping.
It sounds like he may be doing reverse sneezing when he sounds like he is choking? Here is a video of a Puggle doing a reverse sneeze and how to stop it. If that is not what he is dong then I would be concerned about collapsed trachea.