Zsteve, you are partially correct that straight through exhausts have the strong tendency to drone because the mufflers dont break up the sound waves. However, as mentioned above you can fix this drone with tuned side branch resonators. This lets you keep the straight through exhaust and get rid of the drone too, best of both worlds with performance, sound and comfort. Side branch resonators reflect the wavelength of drone back at itself at a quarter the wavelength and effectively cancel out that frequency. Since the drone is actually the pipe resonance frequency echoing in the cabin, you eliminate drone by targeting the frequency at which the resonance occurs.
