I have just tried out my "new", second hand Mamiya 7 camera and am astonished how quiet the shutter mounted in my 65mm lens is, having used leaf shutters on large format cameras. It was so quiet this morning that I assumed the camera wasn't working, but when I looked at the lens whilst firing it it worked.
Are all the lenses for this camera as quiet? If so, it would make an excellent documentary camera. :)