When introduced, the Mazda MX-5 Miata was hailed as the rebirth of the classic sports car/roadster, and in 20 years, it has remained true to that mission. Originally, it was designed and equipped for sporty driving with very little in terms of amenities, but over the years, small concessions were made to drivers wanting a little more comfort. Even in the latest incarnation, introduced in 2006, the MX-5 is a driver's car with a low emphasis on factors such as road noise reduction. However, there are some steps you can take to reduce road noise.
Buy the MX-5 with a power retracting hard top (PRHT). This design replaces the standard vinyl or fabric top with a multiple-piece metal roof. The PRHT has a slightly different profile because of the roof housing and costs more, but the benefits include a reduction in wind and road noise.
Order an accessory hard top for soft-top MX-5s. This optional hard top will provide some of the same noise-reduction benefits of the PRHT model. The accessory hard top is a "semi-permanent" installation, in that it can be removed and reattached but is large enough and complex enough that a driver would most likely attach it for seasonal use when "top down" days are not expected.
Replace the original equipment tires. The MX-5 comes with high-performance tires, befitting its role as a sports car. However, one trade-off for the grip that these tires yield is increased road noise, often manifesting as a "howl" or "warble" that increases in intensity as the car goes faster. Sometimes this is an indication of worn tires, but performance tires often are just simply louder than other types of tires. Owners can consult resources such as the Tire Rack for lower-noise alternatives to the original MX-5 tires.
The MX-5 Miata is a sports car. It's intended to connect the driver with the road and provide a driving experience that most vehicles can't match. Therefore, the driver must expect road noise above that experienced in normal passenger cars. If the noise, vibration and "harshness" of the MX-5 is considered unacceptable, then the best solution is to trade it in on a larger and more comfortable car.