When the engine bushes are worn out ( i hope I understood what part you are talking about, isnt that the rubber thing that absorbs the engine's vibrations? ) you hear a "clunk" noise usually at low speeds, when changing gear or pushing or releasing the accelerator suddenly.
A way to test it is: Turn of the engine and put first gear. Leave the handbrake down. Open the bonnet, and try moving the car with your hands ( 1st gear enganged, handbrake not enabled) forwards - backwards as much as possible. You will hear a clunk noise from the engine's base. A visual inspection is also necessary (at a friends Saxo it happened once a similar noise but it was coming from a loose exhaust connection near the cat.)