Normally, I read slower and experience an internal voice. It is different from hearing a voice with my ears. Not just quieter, but different in a way I can't put into words. Yet also similar.

If I either speed up, or consciously suppress it, I can read without the internal voice, but comprehension goes way down. There's some comprehension, but it's pretty ineffective overall.

If I'm in a relatively quiet place, I don't move my lips or tongue. If I'm in a very noisy place, moving my lips/tongue seems to help.

I once knew someone who said she could not read at all without whispering the words to herself.