The spate of unexplained health problems among the US diplomats led doctors at the University of Pennsylvania to run tests on almost two dozen embassy staff. In March last year, the team concluded the diplomats had suffered concussion-like injuries, but other medical professionals have challenged the conclusions, claiming the doctors misinterpreted the test results.

Not all of the affected diplomats reported unusual sounds when they fell ill, and descriptions of any noises differed from person to person. Some recalled grinding or cicada-like sounds, while others experienced buffeting like that caused by an open car window.