So I just noticed that kind of a strange thing - if you have a ticking clock in your room and you happen to be in complete silence, try concentrating your attention on the ticking sound and just wait. After some time you'll probably notice that the volume of the ticking sound is varying from almost-not-heard-at-all level to a-bit-too-loud level. And sometimes the volume just like goes to 0 and you can't hear anything despite your efforts. And it's kind of creepy when you've got a ticking clock with actual hands - you can see the hands moving and you await a sound to be heard, but it isn't.
Try this, I hope you'll find it at least a tad interesting.
Maybe you have something similar to share? Post it if you do.