grumble grumble /ˈgrʌmbəl/

noun

1. () A loud low dull continuous noise  ( rumbling , grumble , grumbling , rumble )
   a loud low dull continuous noise
    They heard the rumbling of thunder
   they heard the rumbling of thunder
   
2. A complaint uttered in a low and indistinct tone  ( grumble , murmur , murmuring , grumbling , mutter , muttering )
   a complaint uttered in a low and indistinct tone
   

verb

1. () Show one's unhappiness or critical attitude  ( grouch , scold , grumble )
   show one's unhappiness or critical attitude
    He scolded about anything that he thought was wrong
   He scolded about anything that he thought was wrong
    We grumbled about the increased work load
   We grumbled about the increased work load
   
2. () Make complaining remarks or noises under one's breath  ( croak , gnarl [Archaic] , murmur , grumble , mutter , chunter [Informal, British] )
   make complaining remarks or noises under one's breath
    She grumbles when she feels overworked
   she grumbles when she feels overworked
   
3. () To utter or emit low dull rumbling sounds  ( grumble , rumble , growl )
   to utter or emit low dull rumbling sounds
    He grumbled a rude response
   he grumbled a rude response
    Stones grumbled down the cliff
   Stones grumbled down the cliff
   
4. Make a low noise  ( grumble , rumble )
   make a low noise
    Rumbling thunder
   rumbling thunder