I have a custom 2.5" cat-back... I have an 18" long, 6" diameter Magnaflow muffler in the main tunnel and then a 12" Vibrant resonator in the side tunnel... There's a little drone when under load (climbing hills, etc) but at cruising you barely notice it. Went on a 1700 mile road trip and my GF never had an issue with any of the sound.
I actually have a couple videos of the sounds on YouTube
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