52-hertz whale
Since I was curious, I took the recording from Wikipedia, which is sped up 10×, and slowed it down 10×: <a href="http://vocaroo.com/i/s0dMCeANPrbX" rel="nofollow">http://vocaroo.com/i/s0dMCeANPrbX</a> (No affiliation, just the first no-reg audio host I found.)<p>Edit: you may need to turn up your volume. Much of it (including the first ten seconds) is pretty quiet.<p>Edit²: I confirm hearing nothing at all using a laptop's built-in speakers; you'll need headphones or external audio.