The mugen twin loop was on my si when i bought it. With stock manifold and resonator. So as stated, it was quiet, and barely noticeable till i floored it.
When i installed my dc header, i wanted it louder, so i had the resonator removed.
Years later i got tired of the droning sound. So i reinstalled the stock resonator.
Now it just sounds nice at light throttle. And then when getting on it, it screams. But has no rasp or crackle at all.
Stock cat at first. Then replaced with magnaflow high flow direct fit.
Cant beat it.