Mac Boot Up Sound
Apple have recently brought back the Mac boot up sound.
If you want to re-enable it on your Mac, open up a Terminal and type:
sudo nvram StartupMute=%00
Hit Enter and then type your password.
If you want to turn it off. type the following into Terminal:
sudo nvram StartupMute=%01
Hit Enter and then type your password.
I am not sure but does it sound a bit different to before?