HAHA! I'll take that bet!!!
Your single data point of "boominess", corroborated by JonB65, might represent a few/some/several/most MYs, but certainly not all!
At age 67, I've not lost any of my hearing (I'm tested regularly). The boominess in my MY was eliminated by adjusting the rubber stops on the rear hatch. For sure, I've not just gotten "used to it", as the boominess just doesn't exist anymore. I've had numerous passengers, all of them fussy, classically trained musicians, 2 reputable recording engineers, who pride themselves on their hearing, and none of them have registered any complaint of "boominess". Rough ride, yes, but no boominess.
I'm thinking there's just enough variance in the manufacturing tolerance of these models that it creates some that boom, others that don't. If it were universal amongst ALL MYs, there would be thousands of complaints, not the few we're reading about here.
I don't doubt the issue exists, I just don't think it is universal.