I can't explain what it feels like to read like this. I don't hear a voice except when my attention is drawn to this, like right now: I'm definitely hearing my voice when I type this, but that's because I'm thinking about it. As soon as I forget this discussion, I'll go back to silent reading mode.
Also keep in mind that right now I'm hearing my own voice, not some narrator's. I'd find it extremely distracting if it was someone else's voice, e.g. if it was a woman's voice if the writer was a woman.
PS: note that as I mentioned in another comment, now that my attention has been drawn to it, I am indeed "listening" to my thoughts as I type this. Maybe this is going all the time and I simply don't notice it normally. What I definitely do not hear is some kind of narrator voice reading carefully enunciated words to me (as an audiobook would be). That would be distracting to me.