I'm running the Apex'i N1 and I love the sound of that. Although it is quite loud no matter what your speed you're running the engine at. But, if you are looking for a pretty quiet system try looking into the DC Sports TCS (twin canister system). From what I hear it's pretty damn quiet and produces a decent gain in HP. Then again, the sys. was for an EX not a DX. Noise ratings were somewhere around 95-98dB vs. my N1 which is somewhere between 105-115dB.