muttering (n.)
- aspiration
- breath
- croaking
- drone
- droning
- exhalation
- faultfinding
- gabble
- gibber
- griping
- growling
- grumbling
- jabber
- malcontent
- mumble
- mumbling
- murmur
- murmuration
- murmuring
- mutter
- rustling
- sigh
- sulky
- susurration
- susurrus
- undertone
- whisper
- whispering