grumble vs mutter

grumble

verb
  • To complain; to murmur or mutter with discontent; to make ill-natured complaints in a low voice and a surly manner. 

  • To utter in a grumbling fashion. 

  • To make a low, growling or rumbling noise, like a hungry stomach or certain animals. 

noun
  • A low thundering, rumbling or growling sound. 

  • The sound made by a hungry stomach. 

  • A surly complaint. 

mutter

verb
  • To utter words, especially complaints or angry expressions, indistinctly or with a low voice and lips partly closed; to say under one's breath. 

  • To speak softly and incoherently, or with imperfect articulations. 

  • To make a sound with a low, rumbling noise. 

noun
  • A repressed or obscure utterance; an instance of muttering. 

  • Peas. 

How often have the words grumble and mutter occurred in a corpus of books? (source: Google Ngram Viewer )