[thstone]

With the car stopped and at idle, you'll hear rattling from under the engine. Then simply push in the clutch. If the rattle is greatly diminished or gone, then what you're hearing are engine vibrations coming through the gearbox.

The LWFW does not fully dampen the engine/drive train vibrations as well as the dual mass fly wheel. Thus, now you hear drive train rattling. Completely normal for a Boxster Spec clutch and aluminum LWFW. Mine does exactly the same.