[Apologies if this is in the wrong forum. Still relatively new! And I wasn't sure if I should use this one, grammar/syntax, or brainstorming]

So I'm in the middle of editing a fantasy story, and instead of writing a verb to describe a character's disapproval, I wrote [MARGE SIMPSON NOISE] as a placeholder. You know which one I'm talking about - that "mmmm" sound. I've yet to find a word that adequately describes it. Grunt? Grumble? All I've got right now is "sound of disapproval", and that doesn't quite do it for me. Suggestions?

While I'm on the topic of "Sounds of The Simpsons", whoever can describe the Sideshow-Bob-steps-on-dozens-of-rakes noise will have my undying gratitude.