The Tactile version is suitable for office/multiple workplaces - not whisper-quiet, but bearable. The Clicky version, on the other hand, is definitely not suitable for offices - sooner or later it will lead to bullying (I have both versions).

Relatively quiet compared to a Razer Black Widow. I have the feeling that my mouse click is significantly louder than the keyboard itself. I hope this helps.

If you've ever heard MX Red Silent Switches:
It is minimally (emphasis on MINIM) louder than those.
In any case, it is considerably quieter than "standard" mechanical keyboards and has neither the click-clack noise of louder mechanical switches nor the "echo" that you sometimes get with high-format mech switches.
And then of course it depends on how hard you hit the keys ;-)