i have a butterfly as well but i dont know the brand, im sorry
my Master has had me wear it when we are out for supper and has turned it on...on FULL...as far as i have been able to tell, no one can hear it...of course, my attention is hardly wandering around the room at that point!
LOL
but i have asked my Master and He assures me that it can not be heard any place where some noise is present