Do I ever! I used to be more self-conscious about it, but I've decided that I like it, so whatever - hey, maybe I'll improve my musical skills from it. I also have a friend that does it sometimes which made me less concerned about it. I still don't do it in front of most people since I don't want to annoy them with it. My mom always used to hum/whistle a lot, and although I can't whistle, I do hum a lot. One thing I've been doing a lot lately is making clicking sounds with my tongue. I'm starting to figure out how to get different sounds and learning how to make "beats" of sorts...keeps me entertained. I think a lot of it is due to my car stereo going out, which makes driving very boring. Other than that there's some sounds that I just really enjoy and I'll listen to/make repeatedly, the rythms can be very entrancing. Someone mentioned zippers, I'll second that.
Dot Matrix printers are great, too. Someone's actually made a synthesizer out of them (which has been exibited in art galleries). You can check it out (with audio samples) here. Some more stuff.
Sometimes loud sounds annoy me, but I also have a tendency to listen to music really loud. I like electronic music, which I think with the repetitive beats could be considered a kind of stimming. I listen to a lot of different styles, but lately I've been into really fast and/or complex stuff - breakcore/hardcore/speedcore/IDM. Sometimes I just listen to it, sometimes it gives me some motivation/energy and sometimes I really get into it and just spazz out. Good times...