sound off in WordNet English dictionary

1. express one's opinion openly and without fear or hesitation
   "John spoke up at the meeting"
   opine  speak up  speak out  animadvert  sound off 
   
2. express complaints, discontent, displeasure, or unhappiness
   "My mother complains all day"; "She has a lot to kick about"
   complain  kick  plain  sound off  quetch  kvetch 
   
3. start playing
   "The musicians struck up a tune"
   sound off  strike up 
   

sound off in English Wiktionary