ok, then you are probably hearing lifter noise and not piston slap. there is updated lifters to correct this problem. here is some info on this problem
Some customers may comment on an engine valve lifter tick noise that occurs after the engine has been shut off for at least two hours. The tick noise may last from two seconds to ten minutes.
Non AFM Hydraulic Valve Lifter
AFM Hydraulic Valve Lifter
Well, I just returned from taking it to the large Chevy dealership about 15 miles from me where I've always had the service on my trucks done. I'm now driving a rental car (under warranty coverage) and they are going to tear my engine down apparently. They heard the noise loud and clear, both the the mechanic and the service writer and it's not normal. Definitely "rotational" and "in the engine", which isn't a good thing.