Your Mac’s startup chime can be loud, especially in an otherwise quiet environment. Apple didn’t want to wake the whole house; it just wanted to make sure you could hear the startup chime, and for good reason.
How to Lower the Volume of Your Mac's Startup Chime
The chime, which usually indicates that your Mac has passed the boot diagnostic test, may be replaced by a series of audible tones indicating various hardware errors, including faulty RAM or EFI ROM (Extensible Firmware Interface Read Only Memory).
Over the years, the tones that a Mac emits when it fails its boot test have become collectively known as the death bells. As creepy as that sounds, Apple sometimes added a little humor to the death bells, as it did with the old Performa series of Macs, which used a car crash sound. There were also one or two PowerBook models that used a rendition of the Twilight Zone theme.
Because the startup tone can provide clues to troubleshooting, it is not a good idea to disable it by muting the tone volume. However, there is no reason to turn the tones up so loud.
