I just bought one of those really cheap flat combs and suddenly discovered that I like the noise and the feel it makes when I run my thumb along the teeth.
New stim! And quite comforting actually. I also enjoy holding a particular unused mouse wheel I have up to my ear and spinning it. It was the expensive one that, of course, my mice wouldn't use. So I washed it and found that I liked the sound. (It's not one of those squeaky ones. It's pure plastic and runs incredibly smoothly. Maybe that's why my mice didn't like it...)