You suggest two possibilities: generated in the head or near the person by EM fields. One could in this case use a microphone to distinguish the possibilities. If it is a sound generated near the person, it shows up on the microphone, if it is in the head, it does not show up on the microphone. If it comes at 40 miles/s or any other sub-lightspeed velocity, that is not EM radiation.

The basic fact is that if the signals are real, they can be explained by physics, which generally obeys Maxwell's equations. If psychic phenomenon is being proposed, you've left the realm of the physical, and an astrologer would be the appropriate specialist to pursue this further.