Im all with toostubborn2fail advice.
I will also throw in, that over the past couple weeks since i added my revised full belly, and additional rear wheel weel inserts.
>
Found Here
Mostly the rear wheel inserts have made a bigger difference than the belly in reduced road/tire/wind noise. Essentially.
Moreover added a resonent dampend material between
>Wheel:Wheel well lining/metal<
With 98% added reduction of high pressure air escaping out the wheel.
There's no easy way to reduce a prefab cars, noise level without Adding minute weight in materials specifically made for sound deadening purposes.