One of the most common complaints from Ricoh Theta users had been its loud chirping shutter sound, which can be distracting in some circumstances. Theta users had been requesting this feature since the original Theta came out, but it was not addressed in the m15 or in the S.
However, in an update to its app yesterday (v.1.5.0), Ricoh finally added an adjustment to the shutter sound, allowing users to change the volume from high, medium, low and OFF. Fortunately, once the shutter sound setting is specified in the app, it is retained by the Theta even when shooting without the app.
To change the shutter sound setting, you need to connect the Theta to the app, and go to the settings menu.