spec clutch stage 2 + LWFW
 

I have installed the parts and for some reason am hearing a rattling sound from underneath right behind the muffler, any explanation to be shared?

Does it rattle more in neutral with the clutch out than in gear with the clutch in? If so, this is a pretty normal situation...LWFWs make a lot of racket.

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.

I havent ever installed a lightweight flywheel in a car and not had a rattle like you describe, its totally normal. It also will take a few takeoffs in first gear to get the hang of it, its different

^ True. I do agree that it's normal. But just to pry, the rattling sound is the normal rattling sound right? Not any excessive sound, yeah?

I have asked the person i bought the items from and he confirmed this is normal. when i pressure the clutch pedal the sound completely disappears and i have also asked around here and its normal apparently.

LWFW chattering
 

is the noise only when the vehicle is stopped and not in gear?
How about when the car is moving and with the transmission in a gear, if you back off on the throttle such that the transmission rotation (via the tire) matches the engine speed, do you hear the noise?