The United States has evacuated some of its staff from its consulate in Guangzhou in southern China after some of them complained of symptoms of brain injury after hearing strange noises.
The first case was reported two weeks ago and the State Department then described the person's experience as "subtle and vague, but abnormal, sensations of sound and pressure,"
Similar and equally baffling cases occured in September last year in the US and Canadian embassies in Havana.
The US accused Cuba of attacking its staff and expelled 15 diplomats in retaliation.
But despite an FBI investigation it's not been proven that there have been any attacks, and if there have been, how they might have been launched.
The acoustic attack theory has also been met with scepticism by many scientists.
A senior neurrologist with the Cuban Academy of Sciences has called for a joint scientific inquiry with both his American and Canadian counterparts.
The US National Academy of Sciences confirmed it has been approached but didn't comment any further.