I'm in my back yard and I can hear what I thought was someone playing with the points on the tramway,
there was a hollow metalic clonking sound very similar to the noise when the spring loaded blades "clonk" back after a flange has run thru them...
After ensuring that there were no ghosts present I discovered it was actually a FROG making the noise. Investigations lead me to discover that it was a "Pobblebonk" of which there are numerous Tadpoles in the pond of introspective introspection.......
So here in after the sound of tramway point blades snapping back into place will be technically refered to as Pobblebonk, not clunk, thunk, thonk or clonk.... In a sentence: the points closed with a loud Pobblebonk....
Here's the said frog performing live on youtube;
http://www.youtube.com/watch?v=F3ivv7pQkWQ