whistling-breeches, n. — Green’s Dictionary of Slang

whistling-breeches n.

also whistlers

[the swishing noise the material makes as the legs brush together]

corduroy trousers.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1938		Detroit Free Press (MI) 11 Dec. Sports 6/5: ‘Whistling breeches’ made of corduroy [...] are tabooed by wise guides [...] Moose and cariboo have exceptionally sharp hearing, and the musical notes of ‘whistling breeches’ are picked up a mile way — [...] and that ends the chance for a shot.
1968		Philadelphia Inquirer (PA) 26 Oct. 23/3: If your thoughts of corduroy go back to the days of whistling breeches, forget it.