Mark two spots an even distance apart from the center of the circle. They should be closer to the center than to the outer edge, but it doesn’t have to be precise. Punch your holes in those spots. It should look like a big button.
Before you add the string, go ahead and decorate it. Don’t glue anything to it though, since we don’t want to change the balance of the circle.
Once that’s done, you can thread the yarn or string through the holes in your circle. Tie the ends together to make a continuous loop and then slide it so you have equal amounts on each side of the circle. Hold the two ends of the string and spin until the string is wound up. Hold the two ends and let it unspin. Iit will begin to vibrate and make noise.