I've been doing a ton of searching and reading on this problem and it seems to be super common. I can find countless threads with "rattle between 2000-3000rpm" in the title. In my frustration I've read most of them and 90% have no fix and just deal w it. To clarify a little it sounds like a hollow very fast paint can rattle. My 01 started the rattle after I rebuilt the engine with forged internals. The FIRST time I had the issue i could replicate the rattle revving outside the car and i could hear it briefly at startup. It would also be worse until the car warmed up and then it'd go away slightly. I ignored it until one 95* day this summer the drivers side secondary chain snapped in a third gear pull. Luckily (I have NO IDEA HOW) I didn't hurt any valves and/or Pistons. Believe me I checked and checked and ended up with a borescope down the intake runners and through the plug holes. It did wash out my cylinders on that side but I put tranny fluid in them and figure they'd be fine. I replaced my timing chains/tensioners/cam bolts and the curved tensioner guides with all Ford parts except the passenger side secondary which was a new MMR tensioner "flip" modification. Changed the oil and the noise was GONE. And I mean it was gone forever i thought. She ran her ass off once again. Now it's back. Not nearly as bad and a little different. It started only after the Vortech install and very first start up with the base tune my tuner sent to get the car down to the dyno. It definitely did not rattle the day I pulled it onto the lift for install. I'm starting to think it's a pulley or the belt tensioner, but idk. I'd pull the belt and drive it but they're such a pain with the Vortech. I have the powercooler kit so the aluminum could be hitting the ac lines when the motor torques to the side. I just rebuilt the entire Vortech head unit because the front seal was leaking also. I AM however running that crappy dayco composite idler pulley that Vortechs part crosses over to. Oil pressure is up at 90psi at cold start, 30 at op temp idle, and 45-90 with throttle varyence so all is normal there. This time the issue is only present in gear, under very light load, between 2k-3k, and at all driving temps. It's not as loud as the last ratttle but does have the same type of sound. If I lay on the gas a little more it's completely gone. Or if I start out anymore than 1/4 throttle I hear nothing until I shift gears I hear it as the motor winds down for a split second. The car is going on the dyno Friday morning no matter what. Hopefully it's just a timing issue within the tune. Lastly, I have a tube K member so I just pulled the oil pan off of the car to install the Vortech oil return line all rods were inspected. Would anyone else agree this has to be something with the Vortech install? Can the tune alone cause a slight rattle? Going to try and get a video posted up as well as some pics of the last repair and my Vortech install. I WILL get to the bottom of this and post the exact cause and the FIX because there are so many unresolved rattles with these motors. Anyone who has had this issue please post up your experience. Maybe we can start a thread with answers for those that are going crazy trying to track this down. Wow Sorry for the super long post, but I wanted to have as much detail as possible.