When you yell or shout, you use your stomach muscles, this in turn would then put more strain on your lower oesophageal sphincter, the muscle at the top of your stomach. It could be the stomach acids that are making you cough.
Also, my daughter is an asthmatic, as a child I would test her ability to breathe etc by asking her to sing a nursery rhyme... I knew by what word in the song she coughed as to how serious her symptoms were that morning.
Ashtma and reflux are thought to be very closely linked. Some refluxers are diagnosed as asthmatics, when really they have reflux and vice versa. But it is known that if someone has reflux, and if they also have asthma, that they will have more episodes compared to someone just with reflux or just with ashtma.
I hope this answers your question for you.