It's possible I'm brain damaged, though I've never been diagnosed as such. And of course it's possible I'm lacking introspection. I've spent years honing introspective skills via meditation, but of course if I have blind spots, I wouldn't know about them.
My conscious lived is experience has always been one in which I have no inner voice. No words, in fact. It's totally silent in my head. (It's not still. I have racing thoughts. But they're non-verbal. They seem to be in some sort of "mentalese.") I neither see words nor hear them. And it's impossible for me to imagine what my voice sounds like unless I actually hear myself speak.
I also can't imagine what my wife or friends sound like. My father died a few years ago, and I now can't imagine his voice. I never could unless I heard it. And now that's impossible.
While I know the ideas I want to express, I have no clue what words I'll use to express them until I hear them come out of my mouth or see them on a page or screen. When I type, it seems like my fingers are making up the words. Obviously, that's not what's happening, but I have no sense at all that my mind chose the words.
I also have never felt authorship of anything I've written, even though I'm a published author. I have no sense at all that I've written this paragraph. It's my ideas--it's what I wanted to say--but it's as if someone else chose the words.
I suspect that for everyone, there's a process that goes something like this: mentalese --> coming up with words --> expressing words via speech or writing.
Some folks have no conscious access to the first step. For them, it's entirely unconscious. (mentalese) --> coming up with words --> speaking or writing.
In my case, for some reason I seem to have no conscious access to the choosing-words part. It must happen, of course, but it seems to be hidden from my conscious mind: mentalese --> (coming up with words) --> speaking or writing.
Until fairly recently I thought everyone was like me. When people talked about seeing or hearing words in their heads (or their "inner voice"), I thought they meant it metaphorically. It's still amazing to me that people can imagine or "hear" voices in their heads. So I have the same impulse as you, except in reverse: Come on! An inner voice? I'm skeptical. (Intellectually, I'm not, anymore. But I still feel the pang of skepticism, because it's so alien to me.)