The Mac startup sound is more than just a sound that the device makes while starting up, it actually indicates if your Mac is working properly or not. If you have not turned down the volume then not hearing the startup tone indicated that there is something wrong with the device. The device may also indicate problems by giving out unusual sounds at startup.
By reading through this piece, you will find out what each unusual sequence of startup tones mean and how you can handle them.
Mac startup sound
The Mac startup sound is very important part of boot process as it lets the user know if the device has passed the POST (Power On Self Test). If the device passes the bootup test you hear the startup tone only once. Not hearing any tone on startup while your system volume is not turned down or hearing multiple startup tones in a different sequence indicates that there may be a software or a hardware problem that needs your dire attention.
Hearing a startup tone every five seconds indicates that Random Access Memory (RAM) is not installed. The reason behind uninstalled RAM may be that the Ram module has been removed or is misplaced from its slot or that the there is no proper connection of the RAM with the logical board. This error will not let your device startup because a Mac cannot function without RAM. You will have to fix this problem as soon as possible.
Data Integrity Check
Hearing the startup tone three times after an interval of five seconds indicates another problem with the RAM. The problem is that your RAM has not passed the data integrity check. This again is caused by an improper connection of RAM with the logical board or misplaced RAM.
Hearing a long startup tone while you press the power button indicates that the EFI ROM is being updated. This is not something to worry about, leave your device alone while the EFI is being updated. If EFI is not properly updated the EFI software may be corrupted.
If you hear three short and three long startup tones followed by another short tone your EFI software has been corrupted. The Mac models for 2008 and later will recover from this corruption themselves else you will have to recover the EFI ROM by using the Firmware restore CD.
If there is no sound while the system starts your NVRAM has been corrupted and you can use the reset the NVRAM to solve the problem.
Make sure you notice the sound your MAC OS X makes at startup to remain aware of potential system problem.