Rig For Silent Running
To this end the Fujifilm company and a number of other manufacturers have included quiet modes in their cameras. Some are more effective than others; in some cases the reduction in sound is not very much - in others it is complete.
As far as silent cameras go I do remember an Olympus EE film camera of the 1960's that had a leaf shutter actuated in some way by electric circuitry. Even with the acute hearing of youth - pre air drills or military rifles - I could not hear it as it was operated.
With the Hasselblad 500-series you had a pre-release of the mirror that allowed you to get that noise over with before firing the shutter - and if you kept your finger on the shutter button afterwards there was no more sound until you were away from the scene.
The Nikon company have Q modes in some digitals - there is a lessening of sound but not complete cessation. The Fujifilm X-100 that I use has near silence and no illumination of the AF helper light nor any flash shot if you press the " DISP" button and hold if for a few seconds.
This is the reason that no-one in the crowd at yesterday's Food Truck Rumble took any notice of me. That and the ghillie suit and the breakdance competition going on and the 30 food trucks and the 50 people lined up in front of each food truck continuously for 9 hours. That's one good thing about overbooked venues and immobile lines of hungry people - they do not move very much at all and you can use much slower shutter speeds.
Hint: after about 30 minutes inching forward in the line some people get tetchy. It's best not to sidle up to them as ask if they're hungry yet...They tend to bite at you...