I think I saw somewhere that the voice is connected to one of the accessibility options but I don't remember which.
I actually hope to disable it. I'm hard of hearing and prefer to read the response on the screen and the mostly-useless-to-me voice could disturb others. So I hope there is an option.
I'll look in the watch app once the new watch is paired and working.
Happened for me don't worry!! Go onto the settings app (ON THE WATCH) and click general and then find Siri and just turn Siri up a bit and that worked. Let me know if it does.