sound off - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Express one's views vigorously and loudly, as in Dad's always sounding off about higher taxes. This expression probably comes from the original meaning, that is, “strike up a military band.” [Early 1900s]