I could see a number of neat sound options:
Harley Davidson Motorcycle
Ride of the Valkyries
Star Wars Theme
Theme from Jaws (both fun and a great warning!)
In reverse - the standard Beep, Beep, Beep that we all know and hate (but it gets your attention).
Blog Make a Frequency Plan Tom Burke 17 comments When designing a printed circuit board, you should develop a frequency plan, something that can be easily overlooked. A frequency plan should be one of your first steps ...