Some residents in Marin County complain of the reoccurring loud sounds at night time, and are concerned as the booms are not believed to be caused by fireworks, ABC7 reported.

“There have been really loud explosions!” Cristina Peralta, who lives with her boyfriend in San Geronimo Valley in Marin County, said.

The loud sounds were confirmed by the sheriff’s office, saying that it was heard at least six times last month.

“I heard one and it rattled the walls of our house. I felt it in my body, my chest, it was so low it sounded like it was coming from underground,” Peralta said.

The latest of the explosions was heard around 10:00 p.m. on Sunday, the Marin County Sheriff’s Office said. Evidence was collected by a deputy, which points that someone had put an unknown device on fire and left a tree damaged.

Like Peralta, another resident also expressed concern.

“Doesn’t sound like fireworks, it’s not a similar sound as fireworks, it’s just a deep rumble boom,” a person from San Geronimo Valley said.

More resources were dispatched by the Marin County Sheriff’s Office to catch the suspects behind the explosions.

“It’s a really disturbing sound and it’s scary to hear that when it’s like 8 p.m. on any given night. I hope who is ever setting them off, if they are explosives, to maybe find another spot to do it, or maybe to stop because it’s really freaking a lot of the neighbors out,” Peralta said.