My car always mad a noise that i attributed to be piston slap. Then i started thinking. First of all when i just start it...its quite...it take about 30 seconds to a minute for it to start "clicking". Here is the winner it doesnt go away untill i start driving. I could have the car idle for 30 minutes and it'll still do it. but once i start driving....gone. Now i thinking lifter(s). I will be having a cam installed soon and i figuered that ill have the intake of...might as well check lifters out. The car only has 9000 miles on it though! Anyway...just tell me what you guys think.

 

I hate to be the one that breaks it to you... but you have to pull the heads on a LS1 to get to the lifters

 

My car is the same way. I believe if i left it idling for 20-30 min the noise would stop eventually but it does dissappear once reved or driving it. Im inclined to think it's still piston slap. I could be wrong though.

 

My car had the slap when I changed the oil at the first 500 miles? It stayed that way until the car got up to temps then went away. It was really bad when it was a cold morning. But I have happy news for me since I have done my cam swap with springs retainers and push rods the noise is completley gone????????????
It does not matter how cold it is it does not make a noise other than more valve train noise but not bad. But the slap is gone I am so happy.!!!!!!!!!!!!!!!!!!!

 

I had a similar noise. I found it to be an injector on the right side, so i replaced the entire side. no noise since.