I say it's just about how you describe it and how the video shows. With the windows down, it's pretty loud.
Seems to be a factor of the pipe size, resonator size/shape and RPM combined with the size of the passenger cabin. For me, however, I'm fine with it. With windows up it's actually hardly noticeable and on the highway at a constant speed it's nearly silent.
The only difference between 304 and 409 is the type of metal it's made with. Both are stainless and shouldn't rust but the 304 will stay shiny and won't slowly turn brown with use. Since it's under the car and all of the options come with 304 tips, I saw no need to pay extra. I don't believe the material has any effect on drone or resonance.
It may be possible to add an additional resonator after the one it comes with to lessen the drone further. Might be worth trying that instead of taking the hit of selling a used aftermarket exhaust.