Silverado 5.3 4x4 automatic. Cold starts (and more so on colder mornings) the engine will rap real bad for about 3 minutes and then quiet right down. Thej it is no problem. Always quiet on restarts. Always good oil pressure. Truck has 250,000 on it but the noise has been with it since I bought it 8 years ago. Oil comes out without grit at oil changes (every 5000). Aldata TSB's from GM claim it's carbon buildup. Did a motovac on the engine with no change. Heard once that it could be piston slap.
Anyone experience the same problem ? I would sure like to know the reason for this. Thanks.

 

Yes the some of the first 5.3 liter Chevy motors had piston slap, brand new. I .dont really think this is much of a problem since you have taken good care of the pickup and the noise goes away quickly.