sound off is a verb meaning "express one's opinion openly and without fear or hesitation". It carries 3 recorded senses.
express one's opinion openly and without fear or hesitation
“John spoke up at the meeting”
start playing
“The musicians struck up a tune”
music
Definitions, synonyms and semantic relations for sound off come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.