grumbling

definition: continuous full and low-pitched throbbing sound
example:
speech part: adjective
synonyms: rumbling
definition: a complaint uttered in a low and indistinct tone
example:
speech part: noun
synonyms: murmuring murmur grumble mutter muttering
definition: a loud low dull continuous noise
example:
speech part: noun
synonyms: rumble

How grumbling is being used?