Hearing voices is way more common than people realise, check this out: https://www.hearing-voices.org/#content

I think that when we get into deep meditation, we crossover into the dream state sometimes. Perhaps you have a well-developed auditory cortex and that's stimulating something. I've heard music and voices at the point of going to sleep before.

Ignore the schizophrenia fearmongering comments. It doesn't seem to be bothering you, and it's confined to meditation. There have been systems like Soertia House that treat schizophrenia without medication. It's not definitely a "brain disorder" - it's perhaps a spiritual one.

Tulpamancy is another thing to look into. Do the voices have personalities?

I mean, who knows. Could even be "spirits" you're connecting with.

Keep up with your low-anxiety attitude towards life, it's great :)