Noun

• S: (n) rumble, rumbling, grumble, grumbling (a loud low dull continuous noise) "they heard the rumbling of thunder"
• S: (n) grumble, grumbling, murmur, murmuring, mutter, muttering (a complaint uttered in a low and indistinct tone)

Verb

• S: (v) grouch, grumble, scold (show one's unhappiness or critical attitude) "He scolded about anything that he thought was wrong"; "We grumbled about the increased work load"
• S: (v) murmur, mutter, grumble, croak, gnarl (make complaining remarks or noises under one's breath) "she grumbles when she feels overworked"
• S: (v) grumble, growl, rumble (to utter or emit low dull rumbling sounds) "he grumbled a rude response"; "Stones grumbled down the cliff"
• S: (v) rumble, grumble (make a low noise) "rumbling thunder"

Adjective

• S: (adj) grumbling, rumbling (continuous full and low-pitched throbbing sound) "the rumbling rolling sound of thunder"