This bridge connects the cities of Richmond, Calif., and San Rafael. 

This bridge connects the cities of Richmond, Calif., and San Rafael. 

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The thrum of a mysterious bass tone kept Richmond residents up from late Saturday night into the early hours of Sunday morning, so much so that the city’s mayor announced his office would offer a $500 reward to whoever could identify the source of the sound. 

Richmond Mayor Tom Butt announced on his online forum Sunday that hundreds of people from Richmond, San Pablo and El Sobrante took to Facebook and Nextdoor on Saturday to complain about an “incessant bass tone beat that kept them up all night.” 

According to the post, some people were so distraught about the noise that they took to “driving around in the early hours of the morning seeking the source.” Some possible causes were listed: an immersive music and light show that was ruled out due to the bass tone continuing after the event ended at 2 a.m., ghostly sounds that sometimes come from the Golden Gate Bridge and even a “worldwide mystery sound” known as The Hum.  

At the end of the post, Butt announced a $500 reward to the person who could clearly identify where the noise was coming from. 

“I did not hear it myself. My wife says I’m as deaf as a stump,” Butt told SFGATE. “But I can tell you that hundreds of other people heard it for miles all over west Contra Costa County, so it was a big deal.” 

Butt says that after receiving tips from three different people, including one person who will be the recipient of the $500 reward, he’s “pretty much solved the whole issue” — and honestly, the event that caused the noise seems like it was a fun time. 

“Turns out that it was an all-night party that started at about 10: 00 Saturday night and went on until at least 9: 00 Sunday morning,” Butt said. 

The event was held at the Richmond Parkway and featured a Brazilian trend known as Deboxe, where trucks and cars completely decked out with multiple subwoofer speakers are parked close to each other and used to throw ferociously loud rave-like parties. 

In an update posted to his forum, Butt posted links to ticket sales for the event, which cost $35 for admission and was held by local Deboxe enthusiasts. 

When asked whether the event had been approved by the city, Butt said that there was “nothing legal about it.” 

Blurry videos of the event posted in Butt’s forum show bumping subwoofers and hundreds of people dancing to electrofunk music under colored strobe lights, with a time stamp of 5: 27 a.m. 

Butt says there were three people who tipped his office about the event, and one of them will be receiving the $500 reward. 

“I told him if he sends me his address, I’ll send him a check,” Butt said.