Unfortunately, even our acting schools are not teaching their students theatre etiquette.
Last year I went to a production of "Reefer Madness" that a local university with a performing arts conservatory put on. I made the mistake of going on the last performance, a Sunday matinee. There was so much yelling and screaming going on in the audience that I was tempted to leave during the opening number. But I thought, "Well, they are basically kids and this is the last performance..."
This year I went to the same school's production of "Assassins" and, while it wasn't the noisefest that "Reefer Madness" was, there was still a lot of whooping going on during the show. I was sitting next to a girl who was in the conservatory and she whooped whenever one of her friends appeared in the show.
Having said that, I save any vocal demonstrations that I feel the need to give until the curtain calls.
When I saw "Wicked" on tour, I don't remember any whooping during the show itself. Though, at the end of "Defying Gravity" such a roar went up that I wondered if a Brazilian Soccer team had scored a goal somewhere in the theatre...
"A coherent existance after so many years of muddle" - Desiree' Armfelt, A Little Night Music
"Life keeps happening everyday, Say Yes" - 70, Girls, 70
"Life is what you do while you're waiting to die" - Zorba