A preliminary study from NASA has confirmed what we’ve all suspected: that buzzing noise from drones is more annoying to humans than noises from cars and trucks, even when the noises are at the same volume.

The study found that listening to drone noises was as if a car were suddenly “twice as close as it had been before,” according to New Scientist.

Researchers played recordings from commercially available drones flying at various speeds and altitudes, and recordings of cars, utility vans, and box trucks. Then, 38 participants in the study were asked to rate each recording on a scale from “not at all annoying” to “extremely annoying.” NASA noted that “very few” subjects were able to identify drone sounds and did not know they were listening to drones. Subjects were told the sounds were related to the “future” of transportation. Researchers also noted that car noises were most likely considered less annoying because we’re used to them. Levels of annoyance were affected by factors including how long the noises went on.

“We didn’t go into this test thinking there would be this significant difference.”

“We didn’t go into this test thinking there would be this significant difference,” study co-author Andrew Christian of NASA’s Langley Research Center in Virginia said. The purpose of the research was actually just to prove that Langley’s acoustics research facilities could contribute to NASA’s study on drones.

“This result casts doubt on the idea that [drone] operators can expect their operations to be greeted with minimal noise-based opposition as long as the sounds are ‘no louder than’ conventional package delivery solutions,” the study concludes.

That may spell bad news for companies experimenting with drone delivery like Amazon and Domino’s Pizza. They might just have to think of another way to make the flying robots less disturbing until drones become more commonplace.