What would deaf people's thoughts sound like?

It very well might be signing... although I think it's more likely that their dreams make use their other senses, just as their waking world does. It's PERCEPTION that matters - and even those of us that have the normal range of hearing don't always dream in sound. What does it "sound" like when you know something? Does it have a sound? Probably not - but you definitely know what you know, whether dreaming or awake.

Maybe they don't think the same way. It's possible that they sort of "see" gestures in their heads instead. I know that when I do something a lot in a short time, it almost feels like my brain is wired to think in terms of that activity. For example, I was a music student and had to practice rhythms a lot in college. If I did it enough in the space of an evening, my mind would start to try to organize rhythms of the sounds I heard and the things I saw almost. I also got really addicted to Sudoku once and experienced a similar phenomenon.

Yes. Signing

they hear the voice of Morgan Freeman narrating their every day lives

That's a very good question and i have wondered that before