I can’t speak for all d/Deaf people, but my background is that I communicate via both verbal and sign language.

When I think, I experience my inner monologue in both my own voice and visual imagery in form of sign language.

Culturally Deaf individuals can have an inner monologue, but it may differ from that of hearing individuals. Many Deaf people think in sign language or images rather than spoken words.

I have read that even many hearing people do not have an inner voice, So I imagine that they do not. Perhaps they see text.

Considering that your brain has thoughts both with and without a voice and that the voice you "hear" is basically a transcoding of your synapses I imagine their "voice" is just not transcoded or is "felt" in other ways. Like, have you ever had a thought and then said to your inner self in your own voice, completely unnecessarily for your already in to the next line in the process? Of is that just me?

As a child I had no inner voice, just feelings and weird "do" commands. I've got ine around 14 yo but my memories from before a mosly feelings and images.

It changed when I learn to read and write properly oddly enough.

My inner voice doesn't actually have a sound. It's like it's me talking, but there are no audio properties. It's more like an internal knowing that takes on my speech.