complain vs sound off

complain

verb
  • To make a formal accusation or bring a formal charge. 

  • To creak or squeak, as a timber or wheel. 

  • To express feelings of pain, dissatisfaction, or resentment. 

sound off

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

  • 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. 

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