I've heard voices before, but only once has it been the voice of someone I knew...that's an interesting situation. I understand that if it's not bothering you then you don't want to take more meds for it, but what if this gets worse and you lose the ability to tell that the voices aren't real? Or what if they begin to take up every waking moment? I have a friend with schizophrenia who hears voices constantly; they keep a running commentary on everything that she does. If that starts to happen to you, it could be quite debilitating.
Take care