I live in a very old and very poorly ventilated house without the luxury of central air conditioning. Recently on an extremely hot night I went to bed with several ceiling and floor fans running, as well as a small window air conditioner. Add to that the bane of my existence- a very loud tinnitus. As I lay in my bed ruminating on prayers, thoughts, ideas, I thought I was beginning to hear whispering. As the turbulent air buffeted my ear drums and the tinnitus added it's own special evil din I began to focus on what I began to think were voices. "Voices", thought I, "hey now, I'm not interested in hearing spirits or voices or whatever...". I started to listen intently and realized my brain was attempting to create coherent sound out of the auditory chaos that was a result of loud fans, motors and that's right, f'ing tinnitus. I quickly stopped paying attention to the noise, readjusted my head on the pillow and lo, the "voices" were gone. It's amazing how the brain works to make sense of the world around it; now this experience makes me wonder if the auditory hallucinations of schizophrenics are assembled in the same manner.
This is just speculation on my part, but I grew up around a schizophrenic. I think it is similar, but one important difference. Your brain was trying to make sense out of random noise. It turned them into voices because that was a similar sound to what you were hearing. A schizophrenic does it the other way around, their brain has a hallucination already chosen, and is looking for something to project it on.
At least that's how it seemed to me. All of her hallucinations were based off the same theme.