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