According to my dictionary, "grumbling" is a complaint about something, but "grumble" is also a complaint about something. I am used to using the "normal nouns - verbs as nouns" not gerund form as a noun. Someone told me that in the following sentences, "grumbling" must be used instead of "grumble", but they can't say why.
We didn't hear any grumbling about the food.
She paid up with some grumbling.
Again, I would use "grumble" instead.