I also deduced that my inner monologue isn't making any sound even though I 'hear' the words. For each word it's like the average of every time you have heard that word. But it's easy to mistake that into hearing the sounds, which is probably what is happening when most people claim to hear their inner monologue.

I think it's absurd to be talking about your inner monologue "making sounds"

I just mean the idea itself is absurd. Obviously nothing in your mind is making sounds.

If you just mean "imagining sounds" I would still question what it actually means.

Maybe they're both the same thing (inner monologue that makes imagined sounds, vs inner monologue that doesnt make imagined sounds)

I think in words, but I do not hear voices.

I can tell the difference, because I can easily imagine voices too, it's like remembering them, but you make them say something else :)

But normally my "inner monologue" is voiceless.

My inner monologue can be visualized as phantasmal gray words floating in a blank black space. When I imagine what that monologue sounds like it is mostly has my own voice but occasionally has no definable voice, or it takes on the lilt of some unknown reader as if it were telling me a bedtime story or reading a poem that it knows by heart.