The Associated Press has obtained and released audio of mysterious sounds that some US diplomats and families heard in Cuba before suffering hearing loss, mild traumatic brain injury, nervous system damage, and balance problems.
The sound is profoundly unpleasant.
The clip comes from some individuals who heard the noises and recorded them. So far, 22 Americans have been confirmed as afflicted, but not all heard anything unusual.
Those that did described a range of different sounds, from grinding noises to blaring audio that could only be heard in certain locations.
People who heard noises did report one sound in common, however: an intense, high-pitched, pulsing, ringing noise. The AP describes it as "like a mass of crickets" or a whine that "seems to undulate, even writhe" and reminds you of nails on a chalkboard.
Here's what it sounds like:
According to the AP's analysis, which they elaborate on in a new video, there are approximately 20 different frequencies embedded in this sound - think of a bunch of piano keys all being struck at the same time.
The sound is located between 7,000 and 8,000 kHz on an audio scale.
The embassy has played the recording for other workers so they know what to look out for and has instructed staff to turn on recording devices if they hear something similar.
Those workers have also been told to move away from mysterious sounds if they encounter them.
Is this sound a weapon?
US personnel in Cuba and their family members (as well as some Canadian government staff and their families) started seeking medical treatment for mysterious ailments in late 2016.
The "attacks", if that's what they were, seemed to stop for a while but then started again, with at least one incident reported in August.
No one has figured out what is responsible for the injuries. The lack of explanation, the strange symptoms, and the fact that a number of affected people reported strange auditory phenomena have led to speculation that the injuries are linked to mysterious sonic weapons.
The diplomats' reports kicked off a search for sonic devices, though none have been found.
And it's still not clear whether this sound is a weapon at all.
It's possible that the devices used to capture this recording didn't catch whatever it was that caused harm, particularly if that damage was caused by the use of very low or high frequencies, also known as infrasound or ultrasound.
Experts maintain that there's no known sonic device that could produce these sorts of effects and be undetectable and sometimes inaudible.
"There isn't an acoustic phenomenon in the world that would cause those type of symptoms," Seth Horowitz, a neuroscientist who wrote the book The Universal Sense: How Hearing Shapes the Mind, previously told Business Insider.
Sonic weapons exist, but for the most part they are "highly visible and easy to avoid," according to Horowitz.
And these particular symptoms are quite severe.
"Brain damage and concussions, it's not possible," Joseph Pompei, a former MIT researcher and psychoacoustics expert, told the AP.
"Somebody would have to submerge their head into a pool lined with very powerful ultrasound transducers."
Cuba has denied involvement in these incidents. The US hasn't blamed the country for the issue, but nonetheless cut its diplomatic staff in Cuba in response.
For now, the mystery continues - with an eerie and irritating soundtrack