I don't have a monologue so much as a dialogue. Especially when it comes to parsing new ideas or resolving internal conflicts, it's necessary for me to give voice to multiple perspectives and talk it over like a conversation. Generally they can either operate together, fusing into one perspective, or take turns, but any time I feel conflicted about something I conceptualize it as a relationship disagreement between the two voices. I think lots of people do this but maybe not to the same extent, for me, they are distinct personalities.

I don't think any voice in my head is like a real voice, I couldn't describe them specifically and I would never hear a voice and think it sounds like an internal voice, it's more like there's the content of what they're saying and then a vibe attached to it. Kinda like old school RPGs where there's the text and then a sound effect at a certain pitch to represent the voice, it doesn't sound like that exactly because there are words, but it's similar in that it's not as detailed as a real voice.

Edit: I just realized that I can actually "hear" Sans Undertale saying "You're gonna have a bad time" in my head, based on the sound effect when he talks, but I couldn't articulate it and if I heard audio of it I think it'd sound different/weird.