Presumably those who meditate to "quiet their minds" are also seeking to drive out remembrance of a scent or feeling, innate thought-feelings (like confusion that's internal to the brain), imagery, and all the other ponderable facets the brain creates?
Why not say "seeing movies" or "feeling emotions" or "imagining smells" or whatever form a specific thought might take though? Seems weird to only consider vocal thoughts.
There are other aspects to thoughts too, like links and non-picturable things that one seems to grasp but aren't present in a sense-based way -- for example a "hypercube that smells of snozzberries", you can't see it, it's not making a sound that you've heard before, the smell is not something you know, etc., but to some extent you still behold it.
I've definitely had it before where I was alone at night and it sounded like I was listening to the radio or something like that. Like nothing directed towards me, but voices cutting in and out about different things.
I suppose it's not hearing voices that makes you crazy, but when you start listening to them and doing what they say...