You have a wonderful opportunity to question your voice and find out. There are a number of people that I have read about who have done this, that is interacted with their subconscious. This can be a verbal interaction, but be ready to expect all manner of curious replies to your questions.
One thing I would suggest, Is not to think that your voice being "just" your own subconscious talking is some form of let down. On the contrary it is an amazing thing to happen and is a fantastic gift. You have an opportunity to "discover yourself" in a way that very few get an opportunity to do.
Bear in mind that the subconscious can be a very fickle beast, that reflects your conscious thoughts, so if you challenge your voice, it could even get defensive.

You might even think about "re-joining" with your voice, embracing it as part of you, which could actually enlighten you with all its knowledge. This is not as far fetched as it may sound. LaBerge talked about a similar thing when accepting his nightmare demons were part of him, and he found they transformed when he accepted them and actually had loving thoughts towards them (find this on Youtube).

(hope that hasn't freaked you out ; -)