Hi Robert,I also run the TTI 3" system with the standard Dynomax mufflers that TTI has with it. I was forewarned that the Flowmaster would be "much louder than it needs to be". Im very happy with the outcome, its loud enough to hear me coming, but quiet enough for being around town also.
As for the resonance subject, there is that for sure but only at a specific rpm range and I chalk that up to normal air dynamics and flowrates reaching a form of turbulence at that given rpm value.
mine is near the 2800-3000+/- range. The solution, drive faster. : ) I think the system was well worth the additional coin(s).
The other 63 MW 'recreation' over here in the UK has a differnt system (possibly Accurate?) which I noticed the other week was a fair bit quiter, with no annoying resonance/drone. Those mufflers were longer than our Dynomaxs. Robert 63 Polara 500 England
Derrick Brown '63 Sport Fury, 4 speed derrickb@xxxxxxx