Sometimes, I really love the Internet. Researching various wacky sleep-related things, I found a thread ( http://www.stevepavlina.com/forums/spirituality-consciousness-awareness/18481-hearing-voices-just-i-am-falling-asleep.html ) on people's sensory experiences during hypnagogia (the transition between wakefulness and sleep, [and vice versa depending on who you ask]).
Oftentimes, when I am drifting off to sleep, I will hear voices. It is usually a string of seemingly unconnected people talking, and I just happen to be listening in. Sometimes it's just a couple words or sentences, at other times it is pieces of a conversation. The voices are never directed at me, at least the ones speaking English aren't; often I hear stuff in other languages, like German or Italian.
The thread posits many explanations, from the boringly scientific "misfiring neurons", to the annoyingly religious "demons trying to get at you". Perhaps it is the "radio" theory, in which during this state, one can tune in to another plane of existence and hear the dead, or just pick up on "audio" from our own plane.
Some say the experience is quite frightening. Personally, I find it incredibly relaxing. I try to hang on for as long as I can, though is very difficult, and often concentrating on it makes it go away.
Many great thinkers and artists have drawn inspiration and/or the solution to particular problems through hypnagogia. As far as I can tell, what I hear is meaningless. It is still a lot of fun, mind you. I recall one time hearing what I assumed to be a board meeting; someone told a joke and everyone was laughing.