[AndrewAZ]

Hold down the "mute" sound key.. Which is F3 when you start up your computer (not sure if this will work with the BT keyboard but worth a try) and it will keep the start up sound from sounding. I always do this when starting up in class just incase I have the sound on or not.. But the real question is why you are shutting down your computer? I just recommend leaving it in sleep, the only time I restart my macs is when they have an update installed other than that they are sleeping.