I have a 2014 Cruze LT 1.4t with the 6spd manual. The transmission was just replaced under warranty and I had them install the SPEC stage 1 clutch along with the Steel SMF. Initially they had some issues with the install saying it was hard to get into gear, and eventually fixed it and said they believe it was something to do with the clutch not being bled properly (they didnt go into much detail).
After I got it back the first thing I noticed after starting it up is this very noticeable rattling noise while idling, it almost sounds like a diesel engine and goes away when the clutch is fully depressed. Also when the transmission is in gear and driving you can sort of hear it too (sort of sounds like a metal on metal rubbing noise), and goes away when the clutch is fully depressed. Also blipping the throttle up to about 1200~ rpms the noise is even worse.
I spoke to SPEC via e-mail and they told me this is normal?
I've uploaded a vid to youtube so you can get an idea of the noise, its hard to capture the sound on my cell camera due to the aftermarket intake and exhaust, but the first 8 seconds its really noticeable.