Most single actions make those noises. You can silence it by holding the trigger back slightly. You will still get a click when the locking bolt snaps up into place.
To cock a single action silently, first fully cock the revovler. (NOTE THIS PLACES A LIVE ROUND UNDER THE HAMMER!) Then lower the hammer to the half cock position. When a shot presents itself, press the trigger as you draw the hammer to fully cocked then let it go forward to engage the hammer notch. Squeeze it off when the sights are aligned.
THIS SHOULD ONLY BE DONE BY THOSE EXPERIENCED IN HANDLING SINGLE ACTION REVOVLERS!