I have searched through all of the rattle posts and can't seem to find my problem. When accelerating in 1st and 2nd slowly, there is no rattle but when I give it some gas, I hear a rattle from 3 to 4 or 5K rpm. I have a high flow cat and 2.25 mandrel bent custom piping with an N1 style muffler. I had a mechanic take a look at the car and he said that it sounded something like an exhaust leak but could not see one. He suggested putting on a resonator to solve the problem. This seems like a good idea to me as the muffler is a bit loud to begin with. My concern is that it will not fix the problem and I will have added a resonator that impedes air flow. If anyone agrees with this solution, can someone recommend a good resonator or are they all pretty much the same?