Recently I saw a demonstration of a formula 1 racing engine playing music by revving the engine at different speeds (imagine how powerful that motor is to be able to speed up/slow down that fast), but I just found this article, which shows how the HP scanjet scanner has a command to do the same thing. Guess the people at HP were bored 
http://www.ganjatron.net/misc/scanjet/scanjet.html
Check out that video.

http://www.ganjatron.net/misc/scanjet/scanjet.html
Check out that video.