This is exactly what the 2013 Navy Yard shooter complained about (Aaron Alexis). He heard voices speaking to him through the walls. He believed people were using “ELF” (extremely low-frequency) waves on him. He believed they were controlling him or harassing him. He believed microwave signals were vibrating his body. Check this out:
https://m.youtube.com/watch?v=x7xGg8Spcyw
While microwave signals can produce audible sound in the 1 to 10 GHz range (it sounds like music) I'm unsure if words can be spoken through this medium. If you watch the video, you'll know what this sounds like. I've heard this noise in my head before and couldn't explain where it was coming from.
Posted by Plane_Razzmatazz_882