One woman said she heard a blast and saw a flash.
"It's constant," she said. "Sometimes it sounds like a shotgun."
Another caller said he had phoned Alhambra dispatch 15 times saying he has been hearing a loud boom every night, sometimes more than once a day. He speculated that it was drug dealers letting their colleagues know drugs are ready.
"They've got to figure out what this is," he said. "This has got to be escalated at this point."
A third caller said he thought people were driving around the city and dropping explosives.
"It's obviously an explosive projected from an automobile," the man told a dispatcher. "It was shaking the walls and then ka-boom!"
Residents Report Mysterious Booms
NBC4 obtained more than 100 calls from residents reporting hearing explosions in the city of Alhambra last year.
The reports are just some of the calls obtained by NBC4 from more than 100 people who reported the mysterious booms, bangs, gunshots, explosions, firecrackers, and M-80s to the city of Alhambra from January through the end of August last year, before the calls stopped.
Most of the calls were to the Alhambra Police Department, while a few were to 911.
The city reached out to officials with the Los Angeles County Public Works Department, Caltech, Union Pacific, the Southern Gas Co., and Southern California Edison last spring, but no one could figure out the source of the booms.
A Caltech scientist checked seismic activity which didn't offer an explanation, said Chris Paulson, the city's administrative services director.
Some speculate that the sounds that shake houses and trigger car alarms are the work of aliens and a job for "The X-Files'" Mulder and Scully.
"We have got to figure out what the hell this is," a caller told a dispatcher last June after saying he had reported the booms 15 times. "In Brazil, that's what they do to send the message that drugs are ready."
Another caller insisted the sounds were coming from someone in a car.
"These guys are obviously driving around town in a vehicle and tossing the explosive out of the vehicle," a caller told a dispatcher in May. "Obviously these people are operating from a vehicle because I know these explosions have been going all over town, ya know?"
A call hotline heated up during a two-minute period in March when dozens of callers reported the sounds.
One caller asked a dispatcher, "Do you guys have any idea what the heck that is?"
Dispatcher: "It could be a transformer."
Caller: "Right. But transformers don't ... I understand what you're saying. But this shook up the house."
Dispatcher: "Right. The transformer, when they do, you know, explode, it is very loud and it could even have a very bright flash of light."
Caller: "Right. Well I'm sitting here in my bedroom and I've got the windows open and I didn't see a light this time. Anyway, I just thought you guys might know what it is."
Following the January-through-August reports, the city hasn't received any further calls about the sounds, suggesting the source might remain a mystery.
"We did not discover any relevant information then, and since there has not been any damage to property or persons as a result of the noise, or any other evidence such as flashes or smoke, and given that it has not been reported in the past few months, we have not pursued this topic further," Paulson said. "Considering that we don't know the cause or source, I don't think we can definitively say it's over."
