PLEASE do not take your vehicle to the "stealership" for this problem, as said above, they will take your money, and then tell you it is "normal" for the LS engines.
I have piston slap in Sara (2001 Z28 40k original miles), and I have had it in my 2004 Chevrolet Tahoe (4.8L 107K original miles), and I have it in my 2013 Yukon Denali (23k original miles).
The "ticking" goes away in the first few minuets, and also keep in mind that the fuel injectors will tick when the engine is operating.
Hell, Sara sounds like a sewing machine when I first start her up.