GM claims its new Terrain has other SUVs beat when it comes to fuel efficiency, and they're citing active noise cancellation -- a concept near and dear to audiophiles everywhere -- as one of the driving factors that puts it 4MPG above the competition. Basically, the Terrain's enlisted a new one-touch "Eco mode" that allows its four-cylinder engine to run at a lower torque, decreasing engine speeds, and thus saving gas. The thing is, this increased fuel efficiency comes with a "low-end frequency boom," which is where the noise cancellation sets in: two microphones built in to the car's headliner detect the boom, prompting a frequency generator to pump counteracting sou
