Well CD, I found this which slightly dispels the myth that a duck doesn't quack at all. You were right CT, you must watch different tv to me.
Does a duck's quack echo?
The short answer is yes, it does. But this is a science myth that has been quoted all over the place.
Professor Trevor Cox and a team at Salford University recently did some research to get to the bottom of the problem with the help of willing volunteer, Daisy the duck. They found that a duck's quack does echo, but it is quite hard to hear the echo because of the quality of the quack sound. A sound that fades in and out (like a duck quack) makes an echo which can become mixed up with the original sound being made. This means it is hard to distinguish one from the other.
The other reason the myth may have arisen is because you don't often find ducks hanging around places where you commonly get echoes, like cliffs on a beach, or large cathedrals!
That could be it. Which in a way is physics.
Margaret