Good question. Personally noticed this phenomenon recently in a very quiet environment- sounded like genuine 'airy noise' rather than being tonal in nature, quite different from the breeze normally blowing in my head
Hardly surprising or alarming, really. If it was EM related, it wouldn't be a far stretch. Our bodies are loaded with polar molecules, which respond by molecular alignment entrained to the switching frequency. The polar-fatty-acid-rich brain I'd imagine is plenty of suitable material to generate some type of neurological noise picked up by the auditory cortex- and other parts of the brain. On the warfare side of things, the non-sound auditory transmission technologies have long dropped out into the public domain. That's a real thing, so it's clear that EM can impart the sensation of audio (among other brain effects).
We're all basically bathing in an ever-deepening field of quickly-switching modulated EM radiation. According to known history, it's unprecedented. Anthropogenic EM emissions are a very different thing from the unmodulated, unswitched natural "DC" sources of various radiation that all life has prior evolved with. Very different. It's the difference between a light that's set on, or off and a light that is strobing at a specific effective frequency to one who is epileptically inclined. So of course, light is nothing new nor is it the risk- the risk is the relatively brand-spanking new manner in how it's modulated and employed, and the trending exponential rate of employment. And the EM bath is relentless.
Really gotta wonder though, if us humans are actually beginning to notice this type of phenomenon, without the genetic determination for EM hearing, then consider the creatures that actually do have EM senses, cetaceans for instance, what in the world are they hearing and at what volume?