the.com/murmuring
Speech kept just below the volume of being held accountable for it.
means Speaking in a low, soft, often indistinct voice — or grumbling complaints quietly rather than aloud.
from From Latin murmurare, to roar or grumble — an echo word imitating the sound of a low, continuous rumble, like a brook or a discontented crowd.
OnomatopoeiaThe word literally sounds like the noise it names.
Heart medicineA heart murmur is blood whispering through a faulty valve.
Starlings tooA murmuration is thousands of birds swirling in sync.