How to Mute the Mac Startup Sound
Many Mac users are fond of the Mac startup sound that chimes on system boot, but there are definitely times when booting that you’d rather just be quiet, say a library or coffee shop.
Temporarily mute the Mac startup sound
If you want to temporarily stop the Mac startup chime sound, just hold down the Mute button on your Mac keyboard, this will silence the boot sound for that particular system boot/reboot.
Note the mute key is going to be different on various Macs, sometimes it has been F3, F10, and on the newest Mac portables, it’s F9. The key looks like a speaker pointed sideways, if you press it while the Mac is turned on you’ll see the following screen:
Note that you will not see that mute logo when the Mac startup has begun, it will simply just be quiet for the startup whenever the key is held down during boot.
Mute the Mac startup sound
If you want a more permanent solution to shut your Mac boot sound up, there’s a preference pane that does just that. WIth StartupSound or StartNinja you can adjust the volume of the startup chime or mute it completely.