To hum or buzz.
To speak or make low, indistinguishable noise; to mumble, mutter.
To say (something) indistinctly, to mutter.
The sound made by any condition which produces noisy, or turbulent, flow of blood through the heart.
A muttered complaint or protest; the expression of dissatisfaction in a low muttering voice; any expression of complaint or discontent.
Soft indistinct speech.
Any low, indistinct sound, like that of running water.