Listen carefully and you can make out slight undulations in a high-pitched whine, like the output of of a swarm of electronic crickets, perhaps.

Believe it or not this is the sound that some American officials believe is to blame for the mysterious illness striking down US diplomats stationed in Cuba.

These alien noises were reported by some embassy staff before they were taken ill with a variety of symptoms, from hearing loss to concussions, leading investigators to suspect that some kind of sonic weapon was being used.

The Associated Press obtained the recording, which is one of several to have been sent for analysis to the US Navy and intelligence agencies.

However, officials say they are no closer to understanding who or what is behind the illnesses.