What's that noise?

I pulled up by Hagley Park tonight to play touch, turned off the car's engine and began to change my shoes. At that point I heard a buzzing, humming, whistling sort of a noise. The radio was off so it wasn't that. It didn't sound like it was coming from the engine. I hunted around inside the car trying to find what could be causing the noise. I opened the door and it got louder so it wasn't in the car. It was too loud and too prolongued to be a puncture though. What was that noise?

I got out of the car and walked over to where we meet to play and the sound got louder and louder. Under the trees it was the loudest. Then I figured it out. Cicadas. Hundreds and thousands of cicadas in the trees, all vibrating their timbals. How can an insect make a noise so loud? I remember sitting in Len & Val's garden the first time I came over to Nuzziland about six years ago thinking the very same thing. If you've never heard cicadas it'll be hard to understand what I'm going on about. But believe me, when they all go at it at the same time it is loud.