Here’s the current lowdown on the truck. They took the valve covers and timing chain cover off and started it up (with shields to catch and return spraying oil), and everything looks fine. Timing chain is pristene, no gear damage, signs of rubbing or anything, great oil pressure, but the noise persists. They can’t seem to pin down where it’s coming from, even though it’s quite loud! They have two clues: The first is that they see a small amount of air bubbling out around the hydrolics that push the timing chain tensioner in, and if they remove the air filter, the sound almost goes away! If anyone has ANY clues what this might be, feel free to give your opinion! So, the truck is still in the shop. They’re going to keep trying to figure it out.