[Cdn17Sport6MT]

Use a square of CLD, (self adhesive) Constrained Layer Damping, constituting about 10% by way of area, versus the rough calc of what the entire doorskin area is. 10 -15% is all u need. Center this square, where tapping on the outside sounds the most tinny. More, and ur just adding needless weight. Also, buy some butyl rope and force it between the anti-intrusion beam and the doorskin. Should sound much better then.

 

[Cdn17Sport6MT]

The quarter panels of my '17 Mazda6 have what sounds like cigarette-paper-thin sheet metal. Now it doesn't oil-can, it doesn't reverberate, but even so I'm inclined to add a square of CLD tile just because... so if I tap it, it'd sound a bit better 🙂. I'm thoroughly unimpressed with Mazda's "cheapness" if you want to call it that, with sheetmetal gauge. Yes, extra thickness doesn't impact drive quality, etc... and actually, thinner, might improve crash survivability... but it seems so, so cheap 😐. Checked out my buddy's '21Jetta. No such cheap feeling. Decent sheetmetal gauge. Mazda makes fragile cars 🙁.