Here's the deal. If I'm at low RPMs (~1,100) and I go from barely open throttle to nearly WOT, I hear a pretty loud rattle. I let someone else hear it and he said that it's probably "valve clatter" and that I should run higher octane. Now, I've also heard that these cars come from the factory tuned for 87 octane and that running higher octane can hurt performance. Anyone have any experience with this? It's still under warranty, so I can take it in to the dealership and let them mess with it, but I'd like to hear what y'all think first. My only mods so far are weld-in Flowmasters, CAI, and a Tri-Ax, so I know it's probably not related to them. I appreciate your help. Thanks.