have opinion vs sound off

have opinion

verb
  • to think; to have or hold as an opinion 

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 have opinion and sound off occurred in a corpus of books? (source: Google Ngram Viewer )