mysterious production of sound

In the summer of 1997, an array of underwater microphones, or hydrophones, owned by the US government picked up a strange sound. For a minute, it rose rapidly in frequency; then it disappeared. The hydrophones, a relic of cold-war submarine tracking, picked up this signal again and again during those summer months, then it was never heard again. No one knows what made the sound, now known as "The Bloop" (hear it at www.thebloop.notlong.com).

- The Bloop