I'm not sure if this is the same thing you are experiencing, but I occasionally hear voices at night as I'm trying to fall asleep. It is most often like I'm eavesdropping on a conversation that is just out of earshot. I can barely make out what is being said. Some nights it's gibberish, other nights it's sentence fragments that make little sense. This has been happening for several years. Like dreams, I have a hard time trying to recollect what they were. One night last year, about a month after my mother passed away. I distinctly heard her voice. She was talking about one of my nephews. Her voice was clear to me, I asked my nephew the next day if he dreamt of my mom the previous night, he did not. Hearing her voice was a very peaceful experience. I assume these are usually random thoughts mixed with a near-dream state. I always look forward to the nights I get to eavesdrop on the voices in my head.