When you were a kid did you ever make a noisemaker for you bike that sounded like a motorcycle? It's easy to do with a trading card (we used baseball cards) and a clothespin. You simply attach the card to your bike frame at the rear wheel using a clothespin and with the card inserted between the bike spokes. If you want a louder sound use more than 1 card stacked together. You can also fold one end of the cards to make them stiffer and stay on better. Play with it and see what works for you. You might be thinking "this sounds great for a kid's bike, but why would I want to do this to my bike?" Because it's fun!!! You won't need to shout "on your left!" when passing someone because everyone will hear you coming!