What is the noun for grumble?

The Word 'grumble' is both a verb and a noun.

The noun 'grumble' is a Word for a mutter in discontent; a Word for a rumbling sound; a Word for a thing.

Examples:

My brother will grumble if I change the radio station. (verb)

The grumble of my stomach tells me that lunch is past due. (noun)

The noun forms of the verb to grumble are grumbler and the gerund, grumbling.