drone.... hmm. to me, that means you get resonant frequencies in the cabin that amplify the volume of the sound..... kind of like the resonant frequency of a ported speaker box will make more Db than a sealed box. Corvettes and Mustangs with Borla exhausts will do this from 1800-2200 or so rpm. right at your cruising speed, even under light load. This phenominon is kind of a growl that is like an engine soundtrack superimposed over your normal engine soundtrack
I have stillen intake, header, cat and exhaust and don't get that phenomenon.
Now.... could you be referring to what others call rasp? That is a phenomenon where you hear the indivual exhaust pulses without them being pressure equalized through an x-pipe to distribute them over both exhaust pipes or to adequately squelch the noise through a highly effective muffler. That phenomenon gives a "blat, blat, blat" sound and gets louder under more throttle and stay around even as the revs climb. Drone tends to go away as the rpm's rise, where rasp is there all the way to the redline.
I don't really hear rasp with my Stillen setup, but when I took the rear muffler section off, it was more raspy than any exhaust I've ever heard. Maybe you're hearing some rasp?
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