Use this Terminal command to install a script that will mute the startup sound.

Unzip the folder (if your Mac doesn't do so automatically) and put it on your desktop. You can acquire it by going to and pressing the Download ZIP button. To mute the startup sound when running OS X El Capitan, you'll first need to download a special script file. However, there's an easy way to deactivate it using a downloadable script file and some short Terminal commands. Sometimes you want to turn on your Mac in an otherwise-quiet room, and unfortunately, there's no built-in way to turn off the sound. We'll answer the second part of the question first: how to make the sound go away. How do I get it back? And if I want it gone again, how do I make that happen on purpose? Answer

I didn't do anything to my audio settings, and the tune always played from day one when I first powered on my MacBook. The ever-familiar tune that plays when I power up my MacBook Air no longer plays, and frankly, I miss hearing it.

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