The Duck's Quack

Did you know that a duck's quack does not echo? And there is no official, scientific answer as to why. Maybe it's because when a duck quacks, it sucks air in rather than pushes air out, so air particles are not displaced externally and hence an echo is not created. I don't know, that's just a guess. But I never took Physics with Mr. Wilhelm so I could be way off base here...