Let out is used with these nouns as the object:
bellow, breath, cackle, call, chuckle, clang, clutch, cry, curse, exclamation, feeling, flat, gasp, giggle, grin, groan, growl, grunt, gurgle, hiccup, hiss, house, howl, laugh, moan, murmur, noise, passenger, peal, roar, rumble, scream, shout, shriek, sigh, snort, sob, squeak, squeal, stream, wail, whimper, whine, whistle, yawn, yelp

Let-out is used before these nouns:
clause