People are trying to figure out why Amazon's delivery trucks sound like a 'demonic crow' when backing up

• The internet's noticing that Amazon delivery vans make a perplexing sound when backing up.
• The sound has been compared to a dying chicken and a crow falling down the stairs while vomiting.

The sound of Amazon delivery vans reversing has been compared to a 'demonic crow,' a flock of murderous hawks, and tortoise sex - but the reason behind the bizarre back-up sound could actually be safety, Input reports.

The harsh, grating sound may be intended to be unique and unignorable to prevent pedestrians, cyclists, and other vehicles from tuning out the sound and getting run into by the Amazon vans, author and freelance journalist Chris Stokel-Walker reports.

"I'm in a large apartment complex and kept hearing that," a commenter on a Youtube video of the van said. "It sounded like a crow falling down the stairs and throwing up at the same time."

Roughly a quarter of all car crashes happen when a vehicle is backing up.

The sound Amazon delivery vans make when backing up is similar to broadband frequency sounds, according to Input. With broadband sounds, it's easier for people in the way of the vehicles to pinpoint where the sound is coming from, and since it's less commonly heard than beeping, people may be more likely to pay attention to it and heed the warning.

"I thought one of my chickens was dying! Turns out it was an Amazon truck," another commenter said. Amazon didn't immediately respond to Insider's request for comment about the sound.

Amazon typically uses Mercedes-Benz Sprinter vans for its delivery vehicles, but it's also begun testing its upcoming fleet of Rivian electric delivery vans ordered in September, 2019, which the company says are easier to get in and out of. Multiple types of delivery vans seem to be making the strange reversing sounds.

"The beep-beeps are annoying, the brain does something called habituation, realizing it's heard the noise several hundred times before," Deborah Withington, a professor at the University of Leeds and founder of Sound Alert Technology, told Input. "You go, 'Oh, for flip's sake, I'm not going to bother responding to that anymore. And of course, it's the one time the vehicle is coming towards you."

Read more over at Input.

Do you work for Amazon or know why its delivery vehicles make that sound while reversing? Contact the reporter at hschlitz@insider.com from a non-work email.