I have only ever fed Tanveer F/T rats and he still managed to get mites so I don't think it has to do with that.
I have no idea where they came from. I got rid of his wood hide several months ago. He has 2 plastic hides now and a fake tree branch. I do use a thin layer of Repti-Bark on a sheet of newspaper for substrate. Oooh I wonder if it was the coconut husk brick I had used before when I was having humidity issues. Hmmmm not sure.