hey all you knowledgeable guys out there. i just had an invidia n1 race cbe and invidia bellmouth catless dp installed on my sti yesterday and it sounds great for the most part. low end is super deep and rumbly, but when i hit around 4500-5500 to redline it gets somewhat raspy, and only if i pin the throttle. if i gradually make my way up to that rpm range, it's just as deep and rumbly, if not more than at the low end. i have no header so its not an equal length issue. my buddy has a 2006 sti with my same setup and it's deep throughout the whole powerband. any ideas what it could be? i spent a sizable amount of money on my parts/install/tune and this is not what it's supposed to be. anyone have ANY ideas of what this is and how to fix it? should i take it to my local subaru shop (not dealer of course), or what? thanks a lot guys.