Apparently actually hearing voices in your head is a sign of a mental disorder, so an internal monologue with an actual voice is concerning.
www.newscientist.com/article/mg22830410-700-are-the-voices-in-your-head-normal/
it isn’t always a sign of madness: our everyday thoughts often sound pretty voice-like. In 2011, Charles Fernyhough and Simon McCarthy-Jones of Durham University, UK, found that 60 per cent of us experience “inner speech” with a back-and-forth conversational quality.
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On the back of their biggest study so far, he and his colleagues estimate that between 5 and 15 per cent of us hear outside voices, even if only fleetingly or occasionally. About 1 per cent of people with no diagnosis of mental illness hear more persistent, recurring voices. Around the same proportion of the population is diagnosed with schizophrenia, challenging the assumption that the two are related.
I talk to myself - debate best course forward - replay conversations or practise ones I may have- have songs playing in my head - rewrite books/characters in films/books - I think that helps me analyse them - think about ideas. I hear and see in my head but can't do smell/taste or touch. If I'm not thinking in words, pictures or music will be playing usually.
I do have a poor working memory can't see words to spell and can't do mental arthimatic in my head but I have a really good episodic memory - maybe that's because things replay in my head?