We're also from the "non-verbal" school, although I've heard a kiai during a particular breathing excercise at my old dojo. Also ran into it lots with Iwama folks, but that's during practice as opposed to warmup.
I'm fond of the quiet during warmup, like the snow gently falling on the field before the battle.... ohhhhmmmmmmm....
Jack
and remember, kiai is just aiki spelled backwards.