murmuring vs muttering

murmuring and muttering both are nouns.

Word	Noun	Adjective	Verb	Adverb
murmuring	Yes	Yes	No	No
muttering	Yes	No	No	No

As nouns, murmuring and muttering are synonyms defined as:

murmuring and muttering: a complaint uttered in a low and indistinct tone

Other synonyms of murmuring include grumble, grumbling, murmur, mutter.

As nouns, murmuring and muttering are synonyms defined as:

murmuring and muttering: a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

Other synonyms of murmuring include murmur, murmuration, mussitation, mutter.

murmuring (noun)	muttering (noun)
a complaint uttered in a low and indistinct tone	a complaint uttered in a low and indistinct tone
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech	a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

murmuring (adjective)	muttering (adjective)
making a low continuous indistinct sound