1
general::
Phrase(s): pipe down
to become quiet; to cease making noise; to shut up. (Especially as a rude command.) • Pipe down! I’m trying to sleep. • Come on! Pipe down and get back to work!
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Stop talking, be quiet, as in I wish you children would pipe down. This idiom is Also used as an imperative, as in Pipe down! We want to listen to the opera. It comes from the navy, where the signal for all hands to turn in was sometimes sounded on a whistle or pipe. By 1900 it had been transferred to more general use.
American Heritage Idioms