a lot of custom exhaust get that sound because it was not done right. close attention should be payed to the bends(mandrel bend are better)to the welds (mig or tig is better)dont butt join and weld,(it leaves welded material on the inside that causes exhaust gas turbulence across it,noise!)better to open the end of the pipe and fit the one coming from the front into it.make sure the fit is tight then mig weld.(less restriction than if the pipe coming from front went over the pipe going back) make sure the muffler is a"true straight through" not 2.5 inlet tip and perforated pipe is a 2"or even a 2.25"(if its 2.5" it must go all the way through as 2.5")at the muffler the welding rule still holds(from front going back the pipe goes into, not outside of the opening after it) another important fact for"strait pipers" there is a maximum length for a given size pipe before the sounds originating("exhaust pulses") higher up reaches resonance "natural vibrating frquency of the pipe itself" after which a resonator has to be put in!case in point: the TRD
kazuma,has a small resonator at the back!it wouldve been even more louder and the pipe vibration"exhaust pulses" would be greater without it.!