Well I finally got around to adding the Stebro X-pipe to the 550 (which didn't fit correctly BTW) along with the Tubi the car has been transformed. Instead of more resonance, I feel that it actually seems to vibrate less since the air moves so much more freely thru the exhaust. The clutch action also seems lighter somehow as the improved throttle response allows you to find just the right RPM for shifting. I highly recommend it for the hard core enthusiats. It may not be to the liking of everyone, but man it sure sounds sweet at full throttle! I am pretty happy with it but now I want the 14 inch Brembo brakes and also plan on lowering it just a tad. V12's rule! It pulled so hard in 3rd, I was blown away.