This is an attempt to listen in on the "inner voice" in your head. This has been demonstrated to me, however crazy this might sound. When targeted, you experience this cicada like sound (or metallic sound) filling your head.
It is already possible to do this remotely. There's tech that allows to point some kind of sonic device at your head from a fair distance and it's possible to hear your inner voice.
I am the victim of this device testing here. For the last year a group of people used sonic device to test interaction with my brain, without my permission, illegally. I have experienced similar symptoms to the ones reported by victims of "Havana Syndrome". I could provide more details, if interested.