One thing I hate from this release is that there is no easy way to turn off the annoying login sound. Hello ubuntu developer? Is it hard to make a tick box in the settings to enable/disable system sounds?

Anyway, while we’re waiting for the developers to fix this issue, we can work this thing out by renaming or removing the sound file of that login sound. Fire up Terminal, then:
$ cd /usr/share/sounds/ubuntu/stereo
$ sudo mv system-ready.ogg system-ready-OLD.ogg

With this, the system won’t be able to find the login sound file, hence it won’t play any login sound.

We can also use this trick to change the login sound with your own sound file, but first we have to convert our sound file into OGG format. The easiest way is using ffmpeg in terminal:
$ ffmpeg -i cool_sound.mp3 system-ready.ogg

Then copy the newly created system-ready.ogg into the directory /usr/share/sounds/ubuntu/stereo.