SAN FRANCISCO (CBS SF) -- Recent windy weather has amplified a new sonic feature of the Golden Gate Bridge when unusually high winds blast into San Francisco Bay, across the iconic span, generating a loud, humming noise that can be heard for miles around.
Friday was the first day the bridge started "singing," at a volume that could be heard across the city, the side effect of a handrail retrofit designed to make the span more aerodynamic on gusty days.
The phenomenon was recorded and posted on social media, with some describing it as "angelic and peaceful," others calling it eerie, mournful or annoying.
"I couldn't really describe the sound," said Brianne Howell of San Francisco. "I think I described it as wind chimes at first and, then, like when you blow into a beer bottle. But then, like multiple beer bottles, because it's different tones."
Is it a hum? A ghostly wail? A Brian Eno-style soundtrack for the world's most beautiful bridge? The noise is not easy to describe. Howell had been chasing the source since April.
"What is that sound," she remembers asking herself walking through the Presidio. "I'm kind of like: am I the only one hearing this?"
"Yeah, I think it was last week and I was a little bit freaked out," said Osa, who regularly crosses the bridge on his bicycle. "Like, is the bridge coming apart?"
"This is part of the wind retrofit project, where we have replaced much of the westside hand rail so that the bridge can be more resilient to really high wind," explained Paolo Cosulich-Schwartz with the Golden Gate Bridge District. "The slats on the new hand rail are much thinner than the old hand rail which means that air can flow more freely across the bridge."
The Golden Gate Bridge District says this was to be expected. During design, the district conducted wind tunnel tests on a scale model of the bridge under high winds.
Friday's very strong winds cranked up the volume, extending the distance the sound carried. People heard it all over San Francisco; some even said they could hear it in Berkeley.
"We had heard it as well in lower wind environments," says Cosulich-Schwartz. "It was a low-level hum, couldn't really be heard outside of the bridge. Then, yesterday is when we experienced the exceptionally high winds where we knew there would be an audible, humming noise."
"Yesterday was so loud," Howell said. "We live in the Outer Richmond and we could hear it from our house."
The rail replacement is about 75 percent complete so the noise could, theoretically, still get a bit louder under the right wind conditions. The district has no plans to change course on the project so the song you heard the bridge sing, is something you will hear again.
"It is new and it will take us all some time to adjust to it," says Cosulich-Schwartz. "It is something we anticipated. It is an interesting new element to an 83-year-old bridge. It's not every day that you can introduce something new to a structure so old."
for more features.