I've had that happen to me a number of times as well, when I'm in between being awake and falling asleep. The voice — usually my mother, and once it was my grandmother — is however inside my head, not coming from the outside. And both my mother and my grandmother have already been dead for ages. My grandmother died in 1994, my mom in 1996 and my dad in 1998.
A number of years ago, I woke up one morning from a painfully loud sound — like an impact from a lightning bolt, and I do know what that sounds like because there was a lightning impact on the tree next to my previous apartment back in 2000, and it was ginormous — but when I asked around with the neighbors during the day that followed, nobody had heard a damn thing. Furthermore, there couldn't even have been any lightning, because it was a bright and sunny day.
I also often have it happen to me that I get woken up from hearing someone ring my intercom. Except that then there's nobody there, and it's usually very late at night, or even the middle of the night. On another occasion, I also had a hand shake my shoulder and wake me up just in time, or I would have overslept, and I needed to go out the door that morning.
Back in the late 1980s, my parents also told me a weird story. My dad was in his workshop behind the garage, which was at the back end of the house, and my mom was all the way over in the living room, at the front of the house. And then they both heard a loud voice calling their name. My mom thought my dad had called her, and my dad thought that my mom had called him. And so they met in the kitchen, at the center of the house, and neither of them had called the other one.
Another weird thing was that, back when I was tending to my dad in 1997 — he was a paraplegic, and he was bedridden, and I was staying over at his house because we thought he was going to die (and he did eventually, but that was more than a year later) — we were both in his bedroom and we could both hear voices. It was usually very late at night, and it would go on for hours. It happened quite a lot, too.
We couldn't make out what they were saying, but it was one man and two women, and the man was doing most of the talking, while the women only occasionally said something, or maybe they were asking a question. But we could both hear it and describe it, and the three TVs at the house were all off. And it couldn't have come from the neighbors either because it was a standalone house.
Now, one could posit that my dad was in an altered state because he was on a prescription syrup that contained both morphine and cocaine — the former for the pain, and the latter to prevent him from slipping into a coma due to the high dose of morphine. He would indeed at times hallucinate wildly because of that junk, but there was no other way to keep his pain under control, and even then it was often not enough. But I myself wasn't on any medication, and I don't do drugs. And I heard it just as clearly as he did.
I've also accidentally recorded voices once on a cassette tape recorder that wasn't receiving any input signal. But that may have had a totally innocuous scientific explanation, because all metal objects can receive radio transmissions and act as a speaker. I've even had it happen several times that the ventilation fan in my toilet picks up a radio station and starts playing music. I've also had the sound of a local radio station come out of the speaker of my guitar amplifier — when it was switched on, of course. Those things are normal and scientifically explainable. But the voices at my dad's house were not.
Lastly, when my mom died, I was standing outside the hospital entrance in order to have a smoke. They had rushed my mom to hospital in an ambulance after first having had to resuscitate her at my parents' house, and they had been working on her for hours already, so I was of course nervous and worried. And then the doctors came out and they told me that she had passed away.
Within 30 seconds after they had left and turned around the corner, I heard my mom's voice call out my name really loudly, at the top of her lungs, like when she was calling out to my brother at lunch or dinner time when he was a little boy and he was playing outside and out of sight. But this time it sounded weird, reverberating, as if the sound came from inside a tunnel and was bouncing off the tunnel walls. There was and still is no doubt on my mind that it was her voice. I even looked around, and there was nobody there. It was a Sunday evening, mid September, at just after 20:00. The street was empty.
I believe that, just as in the case of electronics picking up radio signals, the brain is a receptor, like an antenna with a built-in amplifier. Except that apart from picking up purely electromagnetic energy, it can also pick up ethereal energy. Well, at least my brain can.