SAN FRANCISCO, Calif. (KRON) — A strange whistling sound heard across the city Friday puzzled many San Francisco residents.

“Can someone explain me why is this eerie sound has been going on for an hour in San Francisco,” one person said on Twitter Friday afternoon.

It turns out, the strange sound is coming from the Golden Gate Bridge.

“The Golden Gate Bridge has started to sing,” the bridge’s Public Affairs Manager Paolo Cosulich-Schwartz confirmed Saturday.

The eerie humming is thanks to the gusty winds blowing through newly installed railing slats on the bridge.

“The new musical tones coming from the bridge are a known and inevitable phenomenon that stems from our wind retrofit project during very high winds,” according to Cosulich-Schwartz. “The wind retrofit project is designed to make the bridge more aerodynamic under high wind conditions and is necessary to ensure the safety and structural integrity of the bridge for generations to come.”

The National Weather Service said a weather station near the Golden Gate Bridge reported sustained winds of 30 to 35 miles per hour, with gusts up to 43 miles per hour Friday. Gusts of 45 to 60 miles per hour were also reported nearby in Marin and San Francisco counties.

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