Turn off the chord that plays when Mac boots up

Try this:

Launch the Terminal app on your Mac (it’s inside Applications > Utilities), paste in the following, then press return:

sudo nvram SystemAudioVolume=%80

If you ever change your mind and want to get the startup sound back, you can reenable it by using this command in the Terminal:

sudo nvram -d SystemAudioVolume

There is a reason for the start up chime.

The Macintosh startup chime is the single note or chord (depending on model type) played when an Apple Macintosh computer is turned on. The sound indicates that diagnostic tests run immediately at startup have found no hardware or fundamental software problems.

Ciao.

There currently is no Apple-supported way to do silence the start-up chime in Mavericks.

I've found this to be a good discussion of the possible methods and their pros and cons.

Grammar Of Dev: My How-To Reminders: Disable Mac start-up chime in OS X 10.9 Mavericks ("Band-Aid" workaround only, for now)

http://grammarofdev.blogspot.com/2014/01/disable-mac-start-up-chime-in-os-x-109. html