I picked up a CPO 2015 SHO beginning of May, it had 52k miles. It had about 1 sec rattle on startup. When i researched the car i read alot about the rattle and about how noisy these engines are in general. After driving it for a month it set a P0020 code and dropped it off at the dealer. Just got a call they are gonna do a tear down of the engine to check timing chain. Phasers, etc. Wasnt expecting to utilize the CPO warranty so soon but hopefully if it's a fairly common issue it'll be addressed and fixed.