This is entirely normal. It's called being in a hypnagogic state and usually happens when you're very tired. Often you'll hear voices of people you've heard throughout the day, see flashes of dream like images which can seem like hallucinations because you're still awake and sometimes see geometric patterns etc. I also sometimes hear blasts of music.

Voices are definitely the most prominent thing for me. I work in an office with lots of loud talkers and sometimes before sleeping will hear all sorts of random nonsense spoken by those prominent voices from my day. Do you perhaps see a lot of faces in the day, are you face to face with lots of people or watch TV shows with multiple faces. It's just the brain processing all that information and trying to make sense of it.

It can be quite scary though and for a long time I didn't know what it was. Turns out it's just the brain doing it's thing. It's amazing how the unconscious mind takes over when we're asleep or entering that state.