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okay boys and girls I have an annoying rattle/knock which seems to be coming from under the valve cover. Only does this on initial start up in the morning. Goes away after 3-5 seconds. What could this be? 2001 silverado 5.3
 
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alot of chevs do this

Um... ask other people who have any where from a 99 even later models 98,97, to your year; about that knock. You will find other people who have the same problems. Chevy has a notorious piston slap they call it, also can be valve trouble, but I hear piston slap. On colder days (includes mornings, temp usually colder) I live in norther Minnesota so i get a good knock for a while. Different metallurgical properties in the cylinder walls and piston itself tend to expand at different rates when heated so you hear a knock until it corrects the tolerances, I found 5w30 motor oil or even synthetic will help (a little thiner oil seats into tighter places the colder the temp), since I live in the cold works this works best, I'm not worried about it its done it since it was brand new, Chevy is aware of it. They chose not to do anything because it didn't qualify as recall material, they just told mechanics how to diagnose it.:great:
 

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I hear the same thing under the hood of my 1999 Silverado. It goes away shortly after starting it. It apparrently isnt to serious because it's been doing it for a long time and I have no problems with the motor.
 
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