My colleague  Jesper was struggling with his HTC 740 phone in order to remove the shutter sound, at long last he found a solution;

Edit the phone’s registry via a registry tool eg. this
and remove the x.wav sound like shown here in an after shot.

On my version (same model maybe a different build) it was a whole lot easier;

  • Start camera
  • Select menu
  • Browse down (about 3 screens) to “Shutter sound” and simply turn it off.