Stomp on the gas in a new Ford Mustang or F-150 and you’ll hear a meaty, throaty rumble – the same style of roar that Americans have associated with vehicle power and performance for decades.

It’s a sham. The engine growl in some of America’s best-selling cars and trucks is actually a finely tuned bit of lip-syncing, boosted through special pipes or digitally faked altogether. And it’s driving car enthusiasts insane.

Fake engine noise has become one of the auto industry’s dirty little secrets, with automakers from BMW to Volkswagen turning to a sound-boosting bag of tricks. Without them, today’s more fuel-efficient engines would sound far quieter and, automakers worry, seemingly less powerful, potentially pushing buyers away.

Softer-sounding engines are actually a positive symbol of just how far engines and gas economy have progressed. But automakers say they resort to artifice because they understand a key car-buyer paradox: Drivers want all the force and fuel savings of a newer, better engine – but the classic sound of an old gas-guzzler.

‘REFINED GROWL’ OR ‘MIND TRICK?’

“Enhanced” engine songs have become the signature of eerily quiet electrics like the Toyota Prius. But the fakery is now increasingly finding its way into even beefy trucks and muscle cars, long revered for their iconic growl.

For the 2015 Mustang EcoBoost, Ford sound engineers and developers worked on an “Active Noise Control” system that amplifies the engine’s purr through the car speakers. Afterward, the automaker surveyed members of Mustang fan clubs on which processed “sound concepts” they most enjoyed.

Ford said in a written statement that the vintage V8 engine boom “has long been considered the mating call of Mustang,” but the newly processed pony-car sound is “athletic and youthful,” “a more refined growl” with “a low-frequency sense of powerfulness.”

Among purists, the trickery has inspired an identity crisis and cut to the heart of American auto legend. The “aural experience” of a car, they argue, is an intangible that’s just as priceless as what’s revving under the hood.

“For a car guy, it’s literally music to hear that thing rumble,” said Mike Rhynard, 41, a past president and 33-year member of the Denver Mustang Club. He’s swayed between love and hate with the snarl-boosting sound tube in his 2012 Mustang GT, but of the computerized noise, he’s unequivocal: “It’s a mind-trick. It’s something it’s not. And no one wants to be deceived.”

KEEPING THE SOUND TRICKS QUIET

That type of ire has made the auto industry shy about discussing its sound technology. Several attempts to speak with Ford’s sound engineers about the new F-150, a six-cylinder model of America’s best-selling truck that plays a muscular engine note through the speakers, were quietly rebuffed.

Car companies are increasingly wary of alerting buyers that they might not be hearing the real thing, and many automakers have worked with audio and software engineers to make their cars’ synthesized engine melody more realistic.

Volkswagen uses what’s called a “Soundaktor,” a special speaker that looks like a hockey puck and plays sound files in cars like the GTI and Beetle Turbo. Lexus worked with sound technicians at Yamaha to more loudly amplify the noise of its LFA supercar toward the driver seat.

Some, like Porsche with its “sound symposer,” have used noise-boosting tubes to crank up the engine sound inside the cabin. Others have gone further into digital territory: BMW plays a recording of its motors through the car stereos, a sample of which changes depending on the engine’s load and power.

Orchestrated engine noise has become a necessity for electric cars, which run so quietly they can provide a dangerous surprise for inattentive pedestrians and the blind. Federal safety officials expect to finalize rules later this year requiring all hybrid and electric cars to play fake engine sounds to alert passersby, a change that experts estimate could prevent thousands of pedestrian and cyclist injuries.

MAYBE NOT SUCH A BAD THING

With traditional engines, some boosters have even celebrated artificial noise as a little added luxury. Without it, drivers would hear an unsettling silence or only the kinds of road racket they’d rather ignore, like bumps in the pavement or the whine of the wind.

Yet even drivers who appreciate the accompaniment have questioned the mission. A SlashGear reviewer who otherwise enjoyed the new F-150 said the engine sound was piped in “arguably pointlessly.”

Which raises a more existential question: Does it matter if the sound is fake? A driver who didn’t know the difference might enjoy the thrum and thunder of it nonetheless. Is taking the best part of an eight-cylinder rev and cloaking a better engine with it really, for carmakers, so wrong?

Karl Brauer, a senior analyst with Kelley Blue Book, says automakers should stop the lies and get real with their drivers.

“If you’re going to do that stuff … own it. Tell customers: If you want a V8 rumble, you’ve got to buy a V8 that costs more, gets worse gas mileage and hurts the Earth,” Brauer said. “You’re fabricating the car’s sexiness. You’re fabricating performance elements of the car that don’t actually exist. That just feels deceptive to me.”