It started with a sound.

with a sound.

People struggle to find the right words, buzzing one person heard, grinding metal another.

Another spoke of piercing high-pitched squeals. Those who heard it starting in late 2016 were Americans in

Havana, Cuba. We've tried to recreate what they say it sounded like as part of our journey to understand this mystery.

One woman says she felt a pulse of pain as she washed dishes in her home. Another woman was woken in her hotel

by a low humming and intense pressure in her skull. Some heard what sounded like cicadas or crickets.

Others felt pressure, sometimes like the baffling of air inside a moving car

with the windows partially down.

When people covered their ears, the sounds did not change.

It was as if they were inside their heads rather than coming from outside.

One person described it as if standing in an invisible beam of energy. At first the sounds were kept a secret. That was because those who heard them carried

their own. They were undercover CIA officers. But soon word was out and with that came questions, confusion and competing theories.

You're listening to assignment on the BBC World Service with me Gordon Carrera.

CBS News, I'm Steve Cathin.

There's concern about the safety of American diplomats in Cuba and the FBI is investigating.

Corresponded Steve Dorsey has more on the CBS News exclusive.

It would be christened Havana Syndrome,

and it soon became clear it was having a real impact on American diplomacy.

Steve, a State Department spokesperson says some U.S. government personnel in Havana on

official duty have reported incidents that have caused a variety of physical symptoms.

The U.S. Embassy had only been reopened in Cuba in 2015 as diplomatic relations were restored after more than half a century of tension between the two countries. But less than two years later, the

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