sound off phrasal verb ( see also ↑ sound )
1 . informal to express strong opinions about something, especially when you complain angrily in a way that other people find rude or boring
sound off about
She’s always sounding off about too much sex in the media.
He should check his facts before sounding off.
2 . American English if soldiers sound off, they shout out numbers or their names to show that they are there