moan vs sound off

moan

verb
  • To say in a moan, or with a moaning voice. 

  • To complain; to grumble. 

  • To grieve. 

  • To make a moan or similar sound. 

noun
  • a low, mournful cry of pain, sorrow or pleasure 

sound off

verb
  • To hold forth about something in an opinionated manner. 

  • Command instructing a person to confirm that they are present or that some other objective has been met. 

  • Command instructing a person to speak up or acknowledge something. 

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