You are not the only one. It happens to me all the times and everytime I see something, I make a comment in my head. The voice is not intrusive like you said, it's my voice and I feel it's mine. Sure, you would have no real control over the voice.
The problem is if you think the voice isn't yours and you have no control of it. And this, if happens after 35 hours without sleep or in a very tired state, I would say there's nothing to worry about. Think about reducing your stress, working with a bit less passion and sleeping 8 hours a day.
If these voice tell you things, you think, doesn't belong to you at all then maybe you need to go see a professional. Check auditive hallucination on schizophrenic, I don't think you have them but it would be great to scare you getbigger.