Last week I started getting a fairly loud tapping noise from the engine. Only when the engine is cold and i'm accelarating, lower rpm's 15-2500. I have allways had the cold engine piston slap at idle, but this is new. The sound goes away once the engine is hot/warmed up. Truck still runs the same, oil pressure is fine,plugs look good. I even dropped the oil pan and changed the o-ring on the pick up tube(the old one was fine though). There was no metal or anything in the pan.Should I be concerned or has my piston slap just evolved to a new level??

 

Sounds very similar to what I began experiencing last winter. The first 2 years my 2000 Z28 was almost quiet. Then beginning last winter, when the temps are below 30, I can hear a very audible tapping noise which lasts maybe 3 - 10 seconds. If I try driving it away without letting it warm up a minute or two, the noise returns under light load, but doesn't last.

Engine seems fine, nothing else is different from what I can tell. Now, all I do is let my car warm up for 2-3 minutes if the temps are below 30. Then I can drive away without any noise. I don't know what you call it - "cold start knock" or piston slap?

I brought it to the dealer, they heard it and told me "noise normal per GM...". I don't like it but at least I have this in writing.

 

I wish mine only last 10 seconds. It's there until after engine is completly warmed up. Even then it may still be there for several minutes of driving.

 

I see you have a 6.0. Piston slap or that ticking sound is more common in those engines.

 

I too have it when i first start my car.
I also have 123K on it though.

 

Check out http://www.pistonslap.com for more info.