split second rattle/knock
 

Hey there everyone. New here and proud owner of a 2003 Silverado z71 package extended cab with 111,000 miles.

Recently I've noticed a split second knock/rattle sound upon startup. What's weird is that it seems to only do it after the truck is warmed up. If I start it first thing in the morning or after it has sit for about an hour, nothing. But if I drive into town, turn it off, and turn it on say ten minutes later it'll knock upon starting up. Not when it's turning over but as soon as it fires up it'll be a quick sudden knocking sound and then be perfectly fine. Literally knocks less than a second and more pronounced inside the cab.

Oil pressure is good and the truck runs great. Any ideas what it could be? Dry starting? Something loose? I've heard stories about the 5.3 piston slap and how noisy this engine can be but it seems to only do it after it warms up? I'm at a loss and some advice would be greatly appreciated, thank you.

Any ideas anyone? I would really appreciate the help.

I know the 5.3's of this era were prone to a little bit of piston slap at cold startup, but that doesn't seem to be what you're describing...

Other than that, without hearing it, I really couldn't guess.

Nice job on scoring a low mile truck tho!