From Longman Dictionary of Contemporary Englishsound off phrasal verb1 informalCOMPLAIN to express strong opinions about something, especially when you complain angrily in a way that other people find rude or boring about She’s always sounding off about too much sex in the media. He should check his facts before sounding off.2 American EnglishPMA if soldiers sound off, they shout out numbers or their names to show that they are there → sound→ See Verb table
Examples from the Corpus
sound about• Present-day sporting heroes tend to spend their off-duty moments sounding off about anything and everything.• People rightly sound off about politics on television and the last two weeks have shown how sharp and articulate they are.• In Banff, he sounded off about windows. 