Earlier this week ExtremeTech published a chapter from their "Hacking Ubuntu" book. The chapter focuses on customizing Ubuntu; it shows you how to change startup music, backgrounds, fonts, icons, ...
Here's a snip:
Logging in for the First Time
When you first log into Ubuntu, a few things will get your attention, like the login music. It's this increasing tone with twinkles that sound like an orchestra tuning up. And the desktop color scheme: brown. Before you can call the system usable, you will need to change these and other things.
Changing the Startup Music
The startup music is one of the easiest items to change. From the menu at the top, select System > Preferences > Sound. This brings up the Sound Preferences applet (see Figure 1). From here, you can assign sounds to system events. For example, I have a blood-curdling scream for error messages, and a telephone ringing for question dialog boxes.