Anyone who's heard a Ferrari V-8 at full wail knows perfectly well that engines make music. But today, that vroom-vroom is getting harder to hear, thanks in equal parts to turbochargers that muffle the noise, increasingly insulated cabins, and government noise regulations.
http://autos.yahoo.com/news/the-rise-of-the-fake-engine-roar.htmlThe new BMW M5, which ditched the sonorous V-10 for a twin-turbo V-8, plays an engine soundtrack through the car's audio system. From a carmaker's perspective, these active sound generators have definite benefits over a sound pipe: There's no need to cut a hole in the firewall or package a separate tube in the already crowded engine bay. Plus, the active devices allow a far greater degree of tunability and can be used to mask unwanted noise.

It remains to be seen just how far automakers will take these systems, but in the future, you may be able to toggle a switch that makes your Prius howl like it's got a V-8.
Just imagine a bricK sounding like a Hog. :hehehe