It's not just flying cars but drones as well. Complaints about the high-pitched keening of propellers could lead to restrictions or regulations that could hamper the growth of a new commercial drone industry.

University of Cincinnati aerospace engineering students are studying solutions to dampen sound in assistant professor Daniel Cuppoletti's lab in UC's College of Engineering and Applied Science. If flying cars are to succeed, Cuppoletti said, they'll have to be quiet.

UC aerospace engineering students Natalie Reed, Matthew Walker and Peter Sorensen presented papers with Cuppoletti at the Science and Technology Forum and Exposition this month in San Diego, California. Hosted by the American Institute of Aeronautics and Astronautics, it's the world's largest aerospace engineering conference.

"I'm looking at noise from a societal impact," Cuppoletti said. "These vehicles have to be imperceptible in the environment they fly in or someone will have to take the brunt of that impact."

Too often, the impact is felt in lower-income neighborhoods, he said.

Airports across the country are the subject of tens of thousands of noise complaints per year filed by aggravated residents. In an FAA survey published last year, two-thirds of respondents said they were "highly annoyed" by aircraft noise. Noise from planes and helicopters were a far bigger annoyance than cars, trucks or neighbors, the survey found.