I've created a simple three-line startup item that silences the Mac OS X boot chime, colloquially known as the "bong" sound, on Intel-based Macs. PowerPC-based Macs use another method for changing the startup chime's volume, so this tip won't work for them.
So why not just run sudo nvram SystemAudioVolume=" " and be done with it? Because of my normal volume settings, my MacBook keeps resetting the chime volume automagically. Until a simpler solution is found (and honestly, three lines is pretty simple), this should work fine. TinkerTool System can silence the startup chime, but it is shareware. StartupSound.Prefpane can do this, too, but DebongIntel is a simpler solution if all you want is to silence the chime. You can also modify the script to set the volume to a non-silent level.
The solution involves making a directory, then two files, then modifying the permissions slightly.
First, the directory (all of the following steps are done in Terminal):
$ sudo mkdir -p /Library/StartupItems/DebongIntel
Next, the two files -- remember to use sudo to create and edit these files.
#!/bin/bash
[ "z$1" == "zstop" ] && nvram SystemStartupSound=" "
File #2: /Library » StartupItems » DebongIntel » StartupParameters.plist:
{
Description = "DebongIntel";
Provides = ("DebongIntel");
}
Finally, the permissions:
$ sudo chown -R root:wheel /Library/StartupItems/DebongIntel
$ sudo chmod -R 755 /Library/StartupItems/DebongIntel
$ sudo chmod 644 /Library/StartupItems/DebongIntel/StartupParameters.plist
This will, in just three "real" config lines and some change, permanently silence the chime. I've tested this on a first generation MacBook running OS X v10.4.8. If you try this on other Intel hardware, please post your results!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070223093835709