Naturally, it could be our subconscious talking to us in the guise of a wise old friend. The objection to that may be that this voice sometimes tells us the answer to problems and questions which have been tormenting us, with a wisdom superior to anything which we have associated with our own intelligence or thinking process.I merely wanted to support the "natural" hypothesis over the "superior wisdom" hypothesis as there is no evidence for this "superior wisdom" and contrastedly, lots of evidence for the "it's your brain, stupid" hypothesis, e.g Persinger and the god part of the brain.
And don't you DARE mention "quantum physics." 
