ok well in my time lurking I've seen people lump a lot of different breeds in with bantams so I know not all bantams are quiet.
Cochins are bantams and apparently very noisy.
I would not consider a silkie to be a bantam but most of the time when someone points out their bantam is loud, they have...
I've got a 3 month old bantam cockerel still inside. He does crow but he is so squeaky I can't hear him a floor down, he will get louder as I have had noisier ones that are outside but even the crows are louder than them and the indoor one is very well behaved, he only crows when I'm around lol...