A low continuous indistinct sound, often accompanied by movement of the lips without the production of articulate speech
English: mutter, muttering, murmur, murmuring, murmuration, mussitation
mutteringEnglish
murmur, murmuring, mutter, muttering, grumble
Noun
A complaint uttered in a low and indistinct tone
English: grumble, grumbling, murmur, murmuring, mutter, muttering