There are two types of thought patterns: verbal and visual.

The majority of people have verbal thoughts, like you say, they hear what they're thinking/reading. Some other people, however, have visual thoughts: they see forms and structures of sentences or objects.

This is, of course, predominantly. We don't have verbal thoughts all of the time and the visual-thinkers don't lack internal monologue, though they struggle a bit to get there.

The thing is: you can't choose. You get what you get. If you're a verbal-thinker, then that's what you'll ever be. You can totally train to read faster, though. There are plenty of tips for that