crazy4c4

ok so over spring break I added a new air filter, fuel filter, pcv valve, Big mouth air dam, and some aero turbine mufflers. Car drove better and did actually run a bit cooler while driving on the highway, it usually stayed a little over 200 and now was a little below 200 while I was driving. However the aero mufflers I put on resonate horribly right at 2000 rpm. I really like the sound outside of the car and as far as performance they helped as much as expected, prob. about 10 maybe 15 hp. I did find out that the owner before me had the cats taken completely out is this the reason for the resonance? The stock resonator is still in place and I really dont want to get new mufflers as it will cost a small fortune to put on corsa. Im thinking about just going with the new 3.73 gears that I wanted anyways so that the car wont be at 2000 rpm on the highway anymore any other suggestions would be great thanks!