murmur vs quetch

murmur is a noun but quetch is not a noun.

Word	Noun	Adjective	Verb	Adverb
murmur	Yes	No	Yes	No
quetch	No	No	Yes	No

As verbs, quetch is a hypernym of murmur; that is, quetch is a word with a broader meaning than murmur:

Other hypernyms of murmur include complain, kick, kvetch, plain, sound off.

murmur (noun)	quetch (noun)
a complaint uttered in a low and indistinct tone
a schwa that is incidental to the pronunciation of a consonant
a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves

murmur (verb)	quetch (verb)
speak softly or indistinctly	express complaints, discontent, displeasure, or unhappiness
make complaining remarks or noises under one's breath