Got my truck back today, dealer removed plugs and checked cylinders with a borescope, saw carbon on all the pistons. So they sprayed combustion chamber cleaner into all cylinders, let it sit, started it up, and the noise is gone. They said GM has never heard of this problem before.

I find it VERY hard to believe an engine could have that much carbon build up after using nothing but top tier premium fuel. Service advisor was trying to tell me it was because I wasn't using dexos spec oil, even though my manual only calls for GM6094M specs and I used full synthetic meeting Corvette specifications.

But the noise is gone and I have 4 years of warranty left so I'm not too worried about it. And yes I am on a 100% stock tune.

 

Carbon build up? Sounds like you need to lay into her more often

 

 

Well that was easy.
they told me to clean the c/chambers myself, which I did, no improvement.

Gm has never heard of that before, hilarious

 

I noticed just a bit of ticking a few days ago in some cooler weather but it has since gone away. Now every time I start my truck I'm expecting to hear the noise. I hope you find your problem and it is easily resolved. After reading the post above about the carbon buildup a dealer found I'm thinking about a catch can....

 

Could the carbon buildup really be caused by oil? Is this what the catch can prevents? If so I think I may have to install one.

 

A catch can properly set up will "catch" oil vapors circulating through the crankcase evac system that eventually accumulate and puddle in the intake manifold. Oil ingestion through the intake system will accelerate carbon buildup but I cannot say to what degree. Ingestion of oil vapors will also polute the intake charge and can rob you of a little power as well, how much I don't know but that is the theory.