Check out this hilarious phonetic analysis of Marge Simpson's signature noise, complete with wav files. Donna accuses me of sounding like Marge sometimes, when I make my version of a noise we both picked up from Caitlin. Unlike the Marge noise, the Caitlin noise isn't just for frustration & annoyance. It's very adaptable. You can use it for enthusiasm, skepticism, irony, &c.