A bizarre sound triggered complaints and insomnia in Richmond over the weekend.
The mysterious sound became such a hot topic in the city that the mayor put out a $500 reward to figure out where it all was coming from.
Tom Butt, the mayor, believes the mystery has been solved.
It all began with hundreds of posts on social platforms of people complaining about a loud, pulsating bass tone shaking their homes.
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Some thought it came from the Craneway Pavillion in Richmond, which held an event on Saturday night. However, the noise lasted until Sunday morning.
That's when the mayor took to his e-forum newsletter to shed light on the problem and offer the reward to anyone with information.
Shortly after, a tip came in.
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"What it is, is people fill up the beds of their pickup trucks with high power sound equipment and then they all get together in one place," the mayor explained. "It's like a rave."
The tipsters informed the mayor that the noise was coming from a Brazilian event which lasted from Saturday night to Sunday morning.
It took place in an industrial part of the city along Richmond Parkway. Not exactly a residential area, but close and loud enough to wake the neighbors.
Danya Champan lives up to road along Richmond Parkway, and while she didn't hear the noise, she hopes organizers would be more considerate next time.
"Not everybody has the weekends off," she said. "Some people have to get up really early, like myself too, and I would probably be really unhappy if I heard that ruckus going on."
The area falls under the jurisdiction of the Contra Costa Sheriff's Office since it took place in an unincorporated part of Richmond.
NBC Bay Area reached out for comment, but have yet to hear back.
"It's water under the bridge now," the mayor said. "I think people are happy to know what it was because it was a huge mystery."
