I'm not an urban planner, but I believe building materials/design acoustics, tree cover, sound barriers all have an impact, as do encouraging non-automotive transport and traffic calming measures.

I'm not saying that eliminating the use of illegal mufflers isn't part of the puzzle. I'm just saying that enforcement is only part of the puzzle, and it's the only part that this group is concerned with. So you shouldn't be surprised that the list they rattled off is "a problem only because of enforcement." That's the lens they're operating from. (Notice that construction noise and sirens aren't on that list even though those are most certainly a noise issue for many many people.)