Non-adhder here. Not constant conversations, no. And not unbidden. I do have conversations in my head, and sometimes they provide answers that weren't readily available to my conscious mind. But I often have "silence" in my mind. When I'm tired enough, that's "no noticeable activity" or "just the steps required to do whatever the immediate activity." Other times it's a song or a "movie" or plans for what I'm doing later.