grumble

To utter or emit low dull rumbling sounds.

“he grumbled a rude response”

“Stones grumbled down the cliff”

Show one's unhappiness or critical attitude.

“We grumbled about the increased work load”

Make complaining remarks or noises under one's breath.

“she grumbles when she feels overworked”

Make a low noise.

A complaint uttered in a low and indistinct tone.

A loud low dull continuous noise.