Title says...most of it. I've got a brand new 2011 WRX sedan w/ 12,000mi on it and I just put an AEM intake, an Invidia catless DP on it and flashed a Stage 2+ map. I also put in Cobb shifter bushings. I drove it for a few days and all seemed well until I went on a road trip and I started to notice a loud, metal, clanging rattle while decelerating especially around 2000-2500rpm. I can hear it a little once in a while in other rpm ranges but it gets very loud and annoying right in that range. Now it is very prominent and I even notice it during easy driving around town. I checked every single nut and bolt I touched while doing my install (twice) and everything is tight. Both of the exhaust gaskets are brand new. I'm totally stumped. I just lifted the car and checked everything again. I decided to add a zip-tie to the O2 sensor wire and took it for a spin; everything seemed fine until about 5min into the ride and the rattle came back full force. Where did I go wrong? Please Help!