Just wanted to let you know that I have the exact same thing. The chatter gets worse when I let it happen and it stops when I'm occupied with something.
Anxiety makes us notice things more, and also, it does make our mind race. If you calm down, the racing mind calms down, too.
I also notice that I get it more when I spend too much time just with myself thinking about stuff. It's almost like thinking makes your mind race even more.
Also I hear you with not being able to distinguish between having an internal dialogue or having psychotic voices. I learned that the main difference is that if we were psychotic, we would hear them with our ears and we would think that these voices are real. As long as you can tell that these voices are in your head, in your own voice, that means they are your own thoughts rather than voices. Also, you stop them if you want, whereas truly psychotic people cannot stop them.