murmur

Any low, indistinct sound, like that of running water.

Soft indistinct speech.

“A murmur arose from the audience.”

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

To grumble; to complain in a low, muttering voice, or express discontent at or against someone or something.

To speak or make low, indistinguishable noise; to mumble, mutter.

“I couldn't hear the words; he just murmured a lot.”

To say (something) indistinctly, to mutter.