Synonyms for Sound Off (same or very similar meaning)
WordNet sense 1 (start playing):
strike upWordNet sense 2 (speak one's opinion without fear or hesitation):
animadvert, opine, speak upWordNet sense 3 (express complaints, discontent, displeasure, or unhappiness):
complain, kick, kvetch, plain, quetchFrom the ODE community, based on WordNetadd/edit