There was a hum that nobody could hear. It was a seismic event, one that originated off the coast of Mayotte on Nov. 11, a tiny island in the waters between Madagascar and Mozambique.
From there, it circled the entire world, though it was unusual enough (un-earthquake-ish enough) that almost no one noticed, as Maya Wei-Haas reported for National Geographic. A few people paid attention though, and that sparked a hunt for the source of the hum that, she reported, still hasn't been resolved.
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