The classic example is fingernails or chalk scraping on a blackboardI have encountered some very interesting ones: rubbing together of a number of materials like styrofoam, balloons, and believe it or not, cotton ballsI discovered scraping a semicylindrical piece of sheet aluminum along its edges, against glass(Gives you the creeps just thinking about it, doesn't it?) Also, chewing aluminum foil.Anyway, have you heard of any other unusual examples? They don't have to be confined to rubbing or scraping examples.
I work as a chef and there are times cleaning meat where the knife scrapes the bone and it almost makes the feeling run up your armI know what you mean with chewing aluminium foil, it makes my teeth hurt just thinking about itEdit-To your edit to Patrick my wife does that to the point we sleep in other rooms unless I fall asleep first, what an awful noise.
