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all NPP mufflers are going to drone in the open position, hence factory,as every after market NPP muffler as well.
Hence basics of a NPP muffler,
So with gate closed, flow is once around the entire muffler, but when gate is open, flow is really straight through the muffler with a short section glass pack that does not prevent the drone isntead.
Corsa sport, and notice that is has resonators that give its the pitch, with no drone.
