muttering muttering /ˈmʌtɝɪŋ/

noun

1. () A low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech  ( murmuration , mussitation , mutter , murmur , murmuring , muttering )
   a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
   
2. A complaint uttered in a low and indistinct tone  ( grumble , murmur , murmuring , grumbling , mutter , muttering )
   a complaint uttered in a low and indistinct tone