I just can't figure out why the truck doesn't do it at every startup after it has sat for an hour or two. I'm convinced the noise is part or all of the valvetrain not getting lubrication for a second or two when it does it...yet it had not done it to me for a week until yesterday, mid-morning, I had to run an errand. It sat for about 1 hour...rattled / rapped as bad as I have heard it. Since then, probably 6 startups later, no noise.