Obnoxious boot chime in OS X? SILENCE IT!

From the terminal:

sudo nvram SystemAudioVolume=%80

To get the chime back:

sudo nvram -d SystemAudioVolume

If you can’t get OS X to boot properly, and are stuck in reboot hell, get to the terminal via Single User mode.  Hold command+S after you hear the chime, or see the grey screen appear after starting your mac.  Then follow the onscreen instructions to mount your main hard drive partition, which consists of this command:

/sbin/mount -uw /

Happy booting in silent peace!!!!