Get a greeting card that plays a cheesey tune like "You Are My Sunshine" and your passport.
Cut the tune generating thingy out. Make sure you don't cut the little plastic tab that glues onto the other side of the card. This pulls a plastic strip from between the circuit breaker contacts as you open the card.
Use stickytape to put the tune thingy in your passport, and stick the plastic tab on the next page. Don't do this on the first page where your photo is. Do it on the second page. Your passport will now play "You Are My Sunshine" or something else, in cheesy single beep tones.
Operation Cheery Customs had begun. The customs officer at Sydney airport told me off for defacing the passport.
Customs Officers have no sense of humour