ALLEN PARK, Mich. --- As an 80 mph wind blew over a preproduction model of the Ford Flex, Steve Dworack heard a buzz.

A small buzz, but a buzz nonetheless, something that could turn off customers who test drive the boxy new crossover vehicle.

Even though it was just two months before the factory was to start cranking out Flexes by the thousands, Mr. Dworack, the vehicle's wind noise engineer, tracked the buzz to a vertical trim piece between the windshield and the pillar that holds up the roof.

The part was replaced with a stiffer one, well worth the $10,000 cost because Ford and other automakers know that buyers equate quiet to quality.

"We basically do whatever it takes to find a solution," Mr. Dworack said during a recent wind tunnel test at a facility that Ford leases in Allen Park, near Detroit.

As automakers work to improve quality, engineers are spending thousands of hours inside wind tunnels, using computers, microphones and their ears to rid vehicles of as much clatter as possible. Wind noise is the No. 1 consumer complaint in the closely watched J.D. Power and Associates initial quality survey.

"They really are obsessive about it, and rightly so, because consumers complain about it," said Dave Sargent, the vice president of automotive research for J.D. Power. "No one can afford to get left behind. If you get a reputation for having very noisy cars, then the natural consequence is people stop buying."

Sometimes the work is painstaking, with engineers placing tape over gaps and pulling it off to find the source of noise.

Much of the early work starts with aerodynamic designs on computers as engineers look to minimize wind drag that can cut into gas mileage. Then they hone the design on clay models and do the final touch-ups on hand-built prototypes.

Ridding a car or truck of wind noise can also help its fuel economy. With $4 per gallon gasoline, automakers are looking for every advantage they can get.

"Anytime you have something generating a noise, what you've got is energy being consumed. And energy consumed is fuel consumption," said Mark Gleason, Chrysler LLC's supervisor of aerodynamics.

Chrysler engineers spent months testing the new Dodge Ram pickup that's due out this fall, making it sleeker and helping to boost fuel economy over the old model. Mileage numbers have not been released.

At Honda, engineers spent hours perfecting the redesigned 2008 Accord's side-view mirrors to keep them quiet yet retain their ability to fold if they hit something. Other automakers have abandoned folding mirrors, but Honda customers have demanded them, said Clement D'Souza, the car's associate chief engineer in Marysville, Ohio.

Honda has used wind tunnel tests over the years to focus on gaps between moving mechanisms such as mirrors and doors. The testing has helped it reduce wind noise complaints in the J.D. Power study from around 12 problems per 100 vehicles on the 1998 Accord to one or two in the newest model, Mr. D'Souza said.

Ford's designers and engineers have worked to tighten the seams between 220 pieces of sheet metal that come together on the Flex. They also have moved the seam between the door and body from the front, where it is on the Expedition SUV, to the side on the Flex. The door is slightly inset from the roof and body, so wind flows over the door, making it more aerodynamic and quiet, said John Wheeler, the Flex's body construction engineer.

The side seam is becoming standard on many Ford models including the Edge crossover and the new Focus, Mr. Wheeler said.

"We do know it makes the vehicle quieter and more robust to manufacturing variations," he said.

The company, like other manufacturers, spent extra money for a sound-deadening windshield on the Flex that has plastic between two layers of glass.

If a car has a lot of wind noise, it's likely a problem with the basic design, and it can't be fixed later on, Mr. Sargent said.

"Chances are you're stuck with that forever. Often there's nothing that can be done about it," he said.

For most automakers, aerodynamic design and noise reduction are taking precedence over other factors including production costs.

"We're advancing the degree of application very rapidly on all our vehicles," said Chrysler's Mr. Gleason. "We don't really have a lot of choice."