The blaring sound, likened to that of crickets, which jolted and sickened several US embassy workers in their Havana residences has been recorded and made available for analysis. The recording was positively identified by employees who say they were subjected to the noise at high volumes, AP reports.
"That's the sound," one of the embassy employees told the agency.
As a result of "attacks of an unknown nature" on 21 embassy staff in Cuba, the US State Department announced the departure of all non-essential staff from the embassy last month.
Investigators have been unable to determine who is responsible or what is causing the injuries. They initially focused their attention on the possibility that a sonic weapon was used, but the mild brain injuries reportedly suffered by some of the victims, such as problems with concentration and verbal memory, are unlikely to be a result of sound.
Some embassy staff remaining in Havana have been provided with recording devices to switch on if they hear an unusual noise. They have also been advised to get up and move to a different room if they suspect they are under attack from a noise.
Last week, the US expelled 15 Cuban diplomats in retaliation at what it sees as Havana's failure to protect staff at the embassy. The Cuban government has denied involvement in or knowledge of the attacks.
"We believe that the Cuban government could stop the attacks on our diplomats," White House Chief of Staff John Kelly told a press briefing on Thursday.