This only happens when the car is ice cold. Any ideas what this could be?

 

Assuming your motor is not actually giving you performance issues, and withi little more to go on than to review the mods you have listed in your sig, it might be related to your CF heat shield perhaps. Have you actually had the hood up on a cold start and tried to pin-point where the source of the "marbles" might be originating?

Certainly IMO your best thing to do would be to have the motor inspected. Although that requires the same cold start you previously mentioned...so you'd need to leave it with the shop for the day, etc.

Good luck!

- Dave

 

Your "marble" description makes me think that what you're hearing is the sound of forged pistons with a dead cold engine, a normal occurance. Is this a new noise? Does it disappear after a couple of minutes? Is it cyclical sound, or a rattling sound. If a rattling marble sound, most likely piston noise. If so, no worries, mine does it, as do many others I've heard at the dealership where I work.

 

Is it possible that the noise is coming from your catalytic converter? That was the source of the 'marbles' in my engine. The material inside the cat shakes around until it gets hot. Eventually it took out my O2 sensor.

 

I just had to have my catalytic converter replaced (38,000 miles) because even though it started out as only a cold start problem it eventually became such a loud and rattling sound that I honestly couldn't stand driving the car. I originally thought it was a loose heat shield or something but the dealer told me the cat was coming apart internally. It's replaced now and it sounds like a new car again. I think alot of people may be having this problem and thinking it is the either the clutch TSB or a heat shield problem.

Do yourself a favor and get it fixed soon because it only gets worse and will drive you nuts!