For me there’s two separate participants, a ‘talker’ and a ‘listener’. My mind identifies more with the talker, because that’s the one that has agency. Since there are two participants, both of which are me, I talk in 1st person plural (‘we’ve got to do …’, 'we thought about this earlier’). I stopped being afraid of being alone after I started having an internal dialogue around the age of 11, since having a second participant in the conversation meant I was always in company.
Edit: Wow, looks like there’s a lot more diversity in this than I was expecting
It’s layered.
At the base level it’s just a mix of a kind of old tv static and what sounds like a creek bubbling. It’s the pre-verbalization soup- textured with sub-thoughts, half-impulses, emotional currents. It’s noticeable background noise but not particularly loud.
Above that is another layer of multiple streams of wordage. Just kind of nonsensical whispers that flow around non-stop. Sometimes there are also impressions of images but nothing definitive. Emotional tones are strongest here.
Above that is the focused wordage, or the internal monologue. Usually it’s proposed point or observation by one “me” and counter-point or add-on by another “me”. There’s no set number of "me"s. Occasionally it’s a construct of some other people I know. Just tangential rambling in incomplete sentences mostly unless I am really trying to sort something out, then it’s more structured. There’s a part of my mind that seems to calculate the conclusion to what I am mentally verbalizing that is one step ahead of the words so often there isn’t a need to complete a thought. This is also where the music and images play.
There is one more layer above all that, the working space, when I really focus, all the other layers fade from consciousness, words are clear, sharp, and coherent and the back-and-forth feels more like a unified “me”, it’s also where I deliberately create and manipulate mental images, movies, concoct scenarios and music plays the clearest.