I have an 02 Yukon and get some noise on startup. I was told it was piston slap although it does sound like lifters. Apparently the GM 5.3 engines are notorious for this. It has something to do I think with some sort of synthetic material used in the piston skirt. There is all kinds of discussion about it on various GM owners threads. The consensus generally is that if only lasts 60 - 90 seconds its alright.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake gate
(previous) 2001 X5, 1991 TriStar 190