Can confirm there is no sound (either when starting or stopping listening using the "Listen then stop listening after recognition completes" option) when using the "Joystick Button Recognition" feature, though there is when using the "Recognition Global Hotkey" option, I.E. the issue seems specific to the joystick option.
EDIT: Correction, it applies to everything but the "Recognition Global Hotkey" option, as the "Mouse Click Recognition" option is also silent.