Here is an interesting website regarding GM's policy and diagnosis on piston slap in their motors. I would be curious as to your responses to this information.

http://www.pistonslap.com/

 

my moms 4.8 does it so does my dads LS1
at first GM said it was a faulty oil pump o-ring that caused aeration of the oil..wheich then caused the "airy" oil to get into the lifters, which caused the tap tap tap

now its carbon buildup at the top of the cylinders..

 

Mine on my truck comes and goes(00, 5.3) , just kinda depends on how recent the oil change was ill change the oil pump and o-ring if i ever do a cam in it

 

I've never bought their stories. Absent evidence to the contrary I am going to have to believe that it's loose piston clearences.

 

If it has a knock sound on cold startup and goes away after warming up, then it is a typical piston slap.. It is nothing to woory about. If the knock noise does not go away after it warms up, it is not a piston slap and could be potentially mean something is seriously wrong with your engine.

As far as piston slap itself..no need to even worry about it. Even my 2000 Corolla has piston slap.

My 94 Z had piston slap
My 3 different 3800 cars had piston slap.. it will not hurt your engine.

 

my moms 3.4 alero does that horribly when cold but never fully goes away.. dealership says its normal and fine. they just dont want to fix it under warrenty.

 

My old 93 Z28 Indy 500 Pace Car always had a slap type of noise to it. It would be worse on some days and really bug me. It was always quieter after an oil change so I believe it really was piston slap. I put 74K miles on the engine (40K with a supercharger) and never had a problem with it. Heck, the SVO 24lb injectors I put in it were louder than the piston slap. I think it's the nature of the hypereutic(sp?) pistons. I wouldn't worry about it unless it sounds like a knock.