This is what Comet 67P/Churyumov/Gerasmenko sounds like, if it's tinkered with a bit so the sound is in a range humans can hear: http://www.iflscience.com/space/rosetta-s-comet-sounds-lot-predator
Pretty cool, I thought. It's easy, on the Internet, to click through things super fast without taking a moment to consider what you're doing. I mean, stop and listen to that. Listen to the whole thing.
This is a rock flying through space, which no human has set foot on. Remotely, we've put a spacecraft near it, and from that spacecraft landed another craft on it to study it. The guy at The Oatmeal illustrated an amusing comparison in some peoples' abilities with regards to this.
But wait, there's more. Some of these were recorded by a space probe in 2001. Again, the pulses or whatever are not in an audible range for the human ear, and so they had to be tinkered with.