I went through exactly the same situation around 10 years ago, but it was about mental imaging. Do you know people can actually visualize and see things when they close there eyes? You probably do, but it took me 25 years to figure out that for most people closing their eyes is not like closing a black curtain.
If that is a surprise to you that people can create and see mental images, you probably have aphantasia as well: https://en.m.wikipedia.org/wiki/Aphantasia
Since then I'm convinced that not two brains experience the world the same way. Inner voice and mental imaging are probably two of the many things we assume to be the norm.