I recently noticed a strange noise on my 99 Impreza Turbo when the car is cooling down.

The clikcing sound one can hear is normal, but every 10 seconds I hear like a "clonggggggg" as if you would hit the brake discs with a spoon or something.
I mention the brake discs as the sound does come from under the car, from the rear somewhere.
I hear it best when is stand on either side of the car.

What could this be? Normal or could there be something letting go?

could be your heat shield on your cat, they creek abit when cooling

Yes, that could be it....how would a creeking sound like?
Sorry, English is not my first language.....

Mine tends to sound a deeper tinnier note than the usual exhaust cooling note which is a bit pingish,sounds more like a small hammer on a small gong, hope you make sense of my description :D

Yup, thats's exactly how it sounds, like a small hammer on a gong...
So, it's only the cat heatshield, nothing to worry about...or could it mean that the heatshield is about to crack?

Now where did i put that crystal ball ;)