i think the noise when you exhale most likely came from instructors wanting to make sure their students were breathing correctly when striking. but like so many other things that happen in MA the instructors never said "hey i am only asking you to scream like a loon so i can be sure you are breathing. you would never actually do this" so everyone learned it that way and consequesntly taught it that way.

they encourage us to make noise at my school but it is so the instructors can know we are exhaling correctly without having to be right next to us. at my old school it was silent. so its still hard for me to abiude by being loud in class.

on a related note and i know this thread is about stomping and not yelling; in tournaments the judges like it when you yell so it reinforces the behavior. if you go to a tournament and don't yell they think you aren't "intense." but then again they might want to know that you are breathing correctly too since air management is a key component of any sport.

so while i think yelling in the privacy of my own home when i am practicing my forms or what ever is absolutely ridiculous i see its merit in a crowded room. (assuming you are in a crowded room practicing with like minded people. other wise you look like a lunatic and sound twice as crazy) but if i tried to yell during sparring for one thing i would lose my mouth gaurd and for another it would be like passing gas in church. it would turn a lot of heads and be really out of place. although it is probably preferable to that whimpering noise i make while i am being pummled. hehe.