I think the EOS 1N is the quiest camera I've ever held...
But I suppose this is subjective. Being profoundly deaf probably doesn't help my recommendation!
But in a tactile sense, it definitely is quiet: solid, business-like, gets it done then finishes. No complaints, and never had people eyeball me if it is bracketing rapidly.
Methinks street photography has a lot of ambient noise and a camera like the 1N is unlikely to make an impression against it.