Hi Folks I had the window down yesterday and I thought I heard the exhaust blowing so I got under the car and pressed the gas and I think it may be blowing close to the engine now I have a custom centre and back box on my Legacy but if I have to go cat back to the centre box will the car have to be re mapped or if I can get it repaired will it still have to be re mapped please advise as money is tight but I dont want to harm the engine many thanks John L.