A recording has emerged of what American embassy workers in Cuba say they heard during what some have billed as a "sonic attack."
The recording published by the Associated Press on Thursday is one of many taken in Cuba since the supposed attacks started last year.
Since then, at least 22 Americans have been "medically confirmed" as affected, but by what is not yet clear.
Cuba has denied involvement in any attacks. The U.S. has not assigned any blame.
In the recording, pulses seem to come in varying lengths with sustained periods that are minutes long.
While some of the affected Americans reported hearing the sounds--often coming from isolated spots in a room--not all those who've been sickened reported hearing sounds.
The AP reports it is also unclear whether all those who heard the sound heard the same sound.
The U.S. says those affected experienced hearing, cognitive, visual, balance, sleep and other problems.
The attacks started last year and have been ongoing, with one incident reported as recently as late August.