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
an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves
Any low, indistinct sound, like that of running water.
To grumble; to complain in a low, muttering voice, or express discontent at or against someone or something.