Possibly a combination of auto suggestion and
EVP or as once widely known,
Raudive Voices, named after
Mr Raudive who popularised the idea.
First read about it in Practical Electronics back in the late 60's when as a teenager and before I knew better I would avidly devour such stuff as in my naivity such things seemed interesting and possibly real manifestations.
People had been claiming over the years to have heard such stuff on tapes in the background noise when cranked up and also when listening between stations on shortwave radio (or VHF without a squelch control), odd broadcasts sounding like snatches of radio transmissions from years ago.
Anyway, I think the accepted wisdom is it's most likely just fluctuations in white noise(and pink) and the brain is making recognisable patterns of what it tries to interpret as speech out of it. We seem to be quite good at doing that, filling in gaps with invented stuff that seems plausible in an effort to make sense of what we think we are hearing (or indeed seeing). Once one person makes this association with a word or phrase, auto suggestion can then sometimes make others hear it too.
There is an ancient track by The Nice called
Diamond Hard Blue Apples Of The Moon that has a lot of white noise in it, Emerson doing his thing and faffing with knives inside a C3, and in a particular few bars of it of it and still to this day, I always hear my fathers voice calling my name out loudly and very clearly. But since this was happening way before he died, while it's odd and was very strange the first time I heard it back in the early 70's, I rationalise it as just psychological, all in the mind, and highly unlikely anything whatsoever to do with voices from beyond the grave.
As an aside, I always thought it would make a great name for a band
The Raudive Voices, but I could never convince my fellow bandmates at the time back then, not
rock enough, though I see someone else now has.
