I couldn't find anything that quite matched this on a search and haven't been around here for a while so here goes...

I'm getting a bit of a rattle/knocking (can't quite tell which it is) when accelerating through 4500-5000k rpms. The noise is the same across all the gears and isn't accompanied by any noticeable power loss or CEL. Also it clears up past 5k and never comes back through redline and I can't replicate it revving in neutral or coasting down. This has been going on for a while (I didn't worry much since it seemed pretty minor). I've owned the car for over 5 years, and have always run it on premium as far as I know.

On a recent trip from L.A. to Tahoe I had an issue with a huge power/torque loss below 4k rpm (including lugging with the gas to the floor) with pretty much normal perfromance above 4k without the 5k computer rev limiter kicking in, but this only happened about about 7000 ft altitude toward the end of the trip and cleared up after an overnight rest. Some of this may have been the result of a half-tank of gas I got at an unfamiliar station in the middle of nowhere, although I'd think that bad gas wouldn't turn good at higher revs.

I've got an '04 (approx 67k miles) with a 6MT and a Rev-i airbox (VFAD duct removed), and had the coils replaced near the end of the warranty and had the plugs replaced at the 60k service (probably still running on the original wires, though), and my last flash update was probably at 60k which was probably last fall.

 

I know this has been dead for a while now, but I think I just found the cause of the problem. Finally got the time and access to put on new plug wires (along with a coil swap), and noticed that the rear-trailing plug wire was hanging loose (and it may have been like that for 2+ years since I bought a new daily-driver in November 09 and have been only driving the -8 on weekends).

most of the knocking is cleared up, but there's still a hint of it when the engine is hot (I'm thinking that plug may be fouled some after about 7500 miles of not firing).