Reference: https://gizmodo.com/no-one-can-explain-the-strange-sounds-making-us-diploma-1826621172 http://dailycaller.com/2018/06/06/state-department-evacuates-more-americans-strange-sounds-china/ There has been a previous incident like this in CUBA. So what does the bright minds on this forum think could be the reason? weapon experiments? unknown terror? The Cuba and China incident indicates that americans are being targeted by "unknown" or that they are doing something at their own embassy that aint all brilliant.
