I haven't used Windows 7 in so long that I don't remember. But Windows has always been eager to make noises on its own initiative. So, always find your way to whatever controls the system sounds and turn them all off if you play cues from a Windows machine. If you don't, it will be only a matter of time before your audience hears a beep, chime, or thud that is going to amuse your lighthing operator, and enrage your stage manager. And no one wants either of those things to happen.