- Distant traffic noise - Hum - Low, indistinct sound - Mutter in discontent - Quietly spoken utterance - Speak quietly - A low, confused, and indistinct sound, like that of
running water.
- Grumble - Mumble - Speak quietly - To utter words indistinctly or with a low voice and lips
partly closed; esp., to utter indistinct complaints or angry
expressions; to grumble; to growl. - To sound with a low, rumbling noise. - To utter with imperfect articulations, or with a low
voice; as, to mutter threats. - Repressed or obscure utterance.