murmur

An abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves.

A complaint uttered in a low and indistinct tone.

A low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech.

A schwa that is incidental to the pronunciation of a consonant.

Make complaining remarks or noises under one's breath.

Speak softly or indistinctly.

“She murmured softly to the baby in her arms”