Grumble (sound) definition

(1) A complaint uttered in a low and indistinct tone

(2) A loud low dull continuous noise

"They heard the rumbling of thunder"

(3) Make complaining remarks or noises under one's breath

"She grumbles when she feels overworked"

(4) Show one's unhappiness or critical attitude

"He scolded about anything that he thought was wrong"

"We grumbled about the increased work load"

(5) To utter or emit low dull rumbling sounds

"He grumbled a rude response"

"Stones grumbled down the cliff"

(6) Make a low noise

"Rumbling thunder"