If you have just upgraded to the latest Mac OS Big Sur, you may noticed the startup sound is back. Every time you boot up your Mac, the special startup sound chimes unless you muted the Mac’s audio before shutting down. Fortunately Apple has the option to allow you to turn this startup audio from the System Preference. Here is how to do that.
Click the Apple icon from the left side of the Mac menu bar to expand the drop-down menu and choose System Preferences. Then click Sound to open the Sound Preferences. Switch to the Sound Effects tab and click the checkmark next to the “Play Sound on Startup” option to unselect and disable the startup audio. This will silence the startup chime the next time you power on your Mac.