Most people expect that a sports car like the Z should be as close quiet like a sedan. The road noise is mostly coming from the oem bridgestone tires.
Had changed the tires to hankook v12 and the noise has greatly reduced. Plus my exhaust is so loud I barely hear any road noise.
But drove a roadster one time I was surprised its more quiet than the coupe even on top down, possibly the clothe top when down insulates the rear trunk which most of the road noise are coming from.