let loose

(intransitive, idiomatic, sometimes followed by with or on) To shout, make a loud sound, or perform a sudden, vehement action; to behave in a raucous, frenzied manner.

Example: 1892, Robert Louis Stevenson, A Footnote to History, ch. 2:
  I can imagine the man . . . prepared to oppress rival firms, overthrow inconvenient monarchs, and let loose the dogs of war.
1916, Arthur Conan Doyle, "A Glimpse of the French Line" in A Visit to Three Fronts:
  May God's curse rest upon the arrogant men and the unholy ambitions which let loose this horror upon humanity!
1963, Margery Allingham, chapter 19, The China Governess[1]:
  When Timothy and Julia hurried up the staircase to the bedroom floor, where a considerable commotion was taking place, Tim took Barry Leach with him. He had him gripped firmly by the arm, since he felt it was not safe to let him loose, and he had no immediate idea what to do with him.
2010 March 27, "Tennis: Venus wins," USA Today (retrieved 22 July 2011):
  Mardy Fish walloped the final shot of the match for a winner, and he let loose a jubilant roar of his own.
1901, Harold MacGrath, The Puppet Crown, ch. 17:
  He set his teeth, and let loose with a fury before which nothing could stand; and Maurice was forced back step by step until he was almost up with the wall.
1965 Nov. 12, "Jazz: The Newest Sound," Time:
  Thus encouraged, the Tijuana Brass let loose with its patented version of The Lonely Bull.
2005 Dec.27, "Report: Jack Black recalls 'lost weekend'," USA Today (retrieved 22 July 2011):
  As if a giant ape weren't enough to get Jack Black going in King Kong, the actor says he let loose one time while making the film.