I just read that Ford spent a lot of effort to make the 2015 Mustang
the most aerodynamic ever. Every detail was tested to eliminate drag. And reduced drag will greatly help with road noise. Also, each engine has its own grill, based on air demand determining the amount of opening. The hood vents are also designed to prevent air flow being trapped under the hood. They even designed it to have air flow hit the wheels at an angle that takes it over the wheel, eliminating the buffeting from the air hitting on the sides. The only way to improve on that is to put wheel covers on it. It is looking like Ford is really putting a lot of effort into this.