grumble - noun

a loud low dull continuous noise

a complaint uttered in a low and indistinct tone

grumble - verb

• show one's unhappiness or critical attitude
• make complaining remarks or noises under one's breath
• to utter or emit low dull rumbling sounds
• make a low noise

grumble - thesaurus

croak   gnarl   grouch   growl   grumbling   murmur   murmuring   mutter   muttering   rumble   rumbling   scold