I think this is a huge part of why I was never diagnosed. I do this thing where I push air out between my back teeth, into my cheek. It creates vibrations that are pretty much IN my ear canal, so it's very loud to me.. but to anyone else, it's just a slight gurgle with a little twist of the edge of my mouth, apparently my mother never noticed it at all, despite the fact that I did it CONSTANTLY as a child. I actually always wondered why nobody ever noticed it, it confused me, because it seems so loud to me, but that's just because it's so close to my eardrum. Sometimes I tried to stop it, but I couldn't for very long, as soon as I'd stop thinking about it, I'd start doing it again.
Anyway.. yes, I do make noises, and it is relaxing and stimulating, although sometimes it tires out my cheek muscles.. but nobody else can hear the noises unless they're specifically watching and listening because I've mentioned it, so it doesn't end up being too embarrassing.. although I caught my reflection in the window the other day, and it actually looks kinda like a smirk..

OMG I think I do the same thing! The way you describe it sounds like what I do. I've never done it around other people though because I always thought they'd for sure be able to hear it. I tend to just do it when I'm alone and bored. I also sometimes make a few other random noises with my mouth but I never know if other people could hear them so I keep them to myself.
As far as other noises, I hum A LOT! Especially while walking. Even if it's just walking two feet to the other room, I immediately start humming when I'm on my feet. This is not usually a conscious choice, I've been asked to stop humming when I didn't even realise I was humming. Other than that I don't really like making noise because I am very noise sensitive and get headaches easily. So when I can have quiet I will cherish it. Though silence is rare because my room shares one wall with a busy street and the opposite wall with the fridge (which has a loud humming noise that kills my head).