A recording has emerged of what American embassy workers in Cuba claim to have heard during what some have billed as a "sonic attack."
The recording, released 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, although the cause — and who might be behind it — 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.
It is also not clear whether the afflicted Americans heard the same sound, The AP reports.
The U.S. says those affected experienced issues with hearing, cognitive, visual, balance, sleep and other problems.
The attacks started last year and have been ongoing, with one an incident reported as recently as late August.