Have you ever wanted your bike to sound like a dirt bike, without having to go through the trouble of taping a card to your bike frame (which by the way is a swell idea), well now you can with a simple pop (soda) can.
Step 1: First Find a Can.
A pop can, beer can, edit: soda can, any 12 oz aluminum can will work. Lay the can down about 10 feet or so in front of your bike.
Step 2: Makin the Noise!
Then ride your bike over the center of the can, the can should go up with your tire and stop.
Step 3: Forewarned.
Be careful though don't ride your bike too long with the can on your tire for it can wear down the treads on your bike. This may not work for all bikes but it could.
Off topic but this is a good hobby,