Personally, my inner voice doesn’t narrate; it only makes logical arguments or explanations. But it does occasionally seem to ‘go on autopilot’: my conscious focus is on some pressing but mindless task, and then I catch my inner voice in the middle of explaining some random trivial thing.
At other times, when I’m in a relaxed and unfocused state, particularly in the shower, my inner voice goes in circles and explains the same thing over and over. This tends to happen when I find an explanation really logically satisfying or interesting. This is perhaps a less interesting situation than the last one, because going through an argument repeatedly to understand it better is probably something that everyone does. But when it goes in circles too many times, I get sick of the topic, and there’s a distinct sense of “will you just shut up already”. Then I have to actively come up with something else to think about.
In both situations, my inner voice is becoming slightly intrusive, acting like a distinct entity from my conscious focus; and it always comes in the form of words even if I’m not actively seeking words. I think that goes beyond just “do I know the words for what I’m thinking”.