verb. ['ˈgrʌmbəl'] show one's unhappiness or critical attitude.
verb. ['ˈgrʌmbəl'] make complaining remarks or noises under one's breath.
noun. ['ˈgrʌmbəl'] a loud low dull continuous noise.
verb. ['ˈgrʌmbəl'] to utter or emit low dull rumbling sounds.
verb. ['ˈgrʌmbəl'] make a low noise.
noun. ['ˈgrʌmbəl'] a complaint uttered in a low and indistinct tone.