I think sound waves bounce off of carbon fiber more completely than stainless steel. Stainless steel absorbs a bit more of the sound wave as it hits, so it muffles the sound slightly better resulting in a deeper tone.
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2012 GM 6MT sports package | FI non res cf exhaust | K&N Drop Ins | Viper 3303 security system w/ tilt sensor | GTR start button | 35% rear 45% side window tint | Michelin PSS
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