murmuring

Adjective

• making a low continuous indistinct sound
  • like murmuring waves
    
  • susurrant voices
    

Noun

• 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

Related words

• Synonyms: 
  susurrant , whispering , grumble , grumbling , murmur , mutter , muttering , murmuration , mussitation