murmuring

nouns

a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
murmur, murmuration, murmuring, mussitation, mutter, muttering
is derived from
murmur
a complaint uttered in a low and indistinct tone
grumble, grumbling, murmur, murmuring, mutter, muttering
is derived from
murmur

adjectives

making a low continuous indistinct sound
"like murmuring waves"; "susurrant voices"
murmuring, susurrant, whispering