It sounds sort of like a mass of crickets. But not quite. A high-pitched whine, but from what? It seems to undulate, even writhe. Listen closely: Some hear multiple, distinct tones colliding in a nails-on-the-chalkboard effect.

The Associated Press has obtained a recording of what some U.S. Embassy workers heard in Havana, part of the series of unnerving incidents later deemed to be deliberate attacks. The recording, released Thursday by the AP, is the first disseminated publicly of the many taken in Cuba of sounds that led investigators initially to suspect a sonic weapon.