Car designers have to fake those sounds. Gearheads are trained to want to hear them, and to equate them with power. However, they're legacy sounds of inefficiencies.
The old glasspack style pop and roar comes from valves closing slowly and incompletely in a mechanically linked engine. It's wasted energy and robs horsepower.
Today's computer timed engines and transmissions, with micromillimeter tolerances, keep all that power contained to the drivetrain. As a result, they don't make much noise. Most of the market for those muscle cars (they still have all the HP to the ground - they just don't need to be loud to do it) doesn't understand this, so the engineers have to design baffles into the exhaust to make noises. At one point, they installed exhaust speakers to play revving noises to fake it.
It isn't just cars. I don't think it's possible to purchase a "regular" truck from Ford or Chevy that doesn't come with a 3" lift and 24" wheels.
