I recently had, while driving, a ten second (or so) period of loud engine rattling and misfire. It cleared up quickly and has been fine for a week. Thinking I had a loss of oil pressure or plugged passage, I pulled the lower oil pan only to find it perfectly clean and no clues. I remembered this issue with the screws and pulled the plenum. I found 2 VIAS plates completely missing and several more screws loose. I know the plates aren't usually ingested, but they are GONE. I didn't believe this, so I popped the spark plugs out and ran a bore scope to find many plate shaped indentations on the pistons (#3 and #4.) Well, I removed the remaining plates and threw it all back together. Now, has anyone else experienced this? I have no idea how the plates made it through. It seems impossible, but I swear to you they were chewed up and spit out. I painstakingly inspected the rest of the plenum, lower intake, and any other areas the plates could have ended up. And the damgage to the pistons speaks for itself. Oh, and the engine runs perfectly with no unusual noises (for 150k + miles.) Although I can't say for how long. Just another story for the pile I suppose...