I'm not sure of anything definitive, but a more credible explanation is that it is some type of sonic monitoring trying to spy upon diplomats via laser microphone or something such, which then happened to actually hurt people.
If you want privacy you can either try to build isolated structures or rooms, or you can try to overwhelm the listener with noise. The US has employed both techniques previously.
What if they were trialing a new defensive (anti-spying) technology that went wrong? The US government has certainly gone strangely quiet on this incident.
...boosting the number of Americans affected this “sonic device” to 25 from 21, with reports of cases occurring in the last several weeks, according to two sources.