The silent "whizz" of a Konica Autoreflex at 1/8th is nice to listen to. Otherwise a Press-Compur from the 50's (you can hear the wheels spinning) or the "kla-chung" of a Mamiya 645 are my favourites.
For me, probably the F. It's a little quieter than the F2 and the F3. But, not when the F-36 drive is in use. :-) BTW: if you want to be reminded as to how an F3 with MD-4 sounds like, just use the camera app on an iPhone. The sound produced by the iPhone is a sample of an F3/MD-4 combo being fired.
Want to be heard with a camera that's not motorized? Try an FM2n, FM3a, FE2, or FA for 35mm, a Hasselblad V-series body for medium format, or a Speed Graphic's focal plane shutter. The Nikon bodies have a definite *CLACK* when fired.
Anyone ever notice that their Japanese camera goes "crick" and German camera goes "schnap"?
The shutter of my Leica II sounds like an insectís whisper.