Also my hunch is that much of the noise might be tire noise.. Since magnetic hover craft RV is years away, I guess I have to live with it. But in some cars, different brand of tires make lots of difference in terms of noise. I am not going to swap out my brand new tires just on hunch.
Anyway..... Have anyone here tried out Sprinter SumoSpring Rear Helper Springs. It is basically big rubber between the suspension and body. Maybe these will help reduce the noise as I drive over expansion joints.
I guess I will eventually just get used to it. But tinkerer / engineer in me wants to give it a shot first.