Updated April 2, 8:45 p.m.
From e-mails to Facebook posts, Castro Valley Patch received several notifications from readers about a loud "boom" that occurred around 10 p.m. Thursday evening.
From shaking windows in their homes to setting off neighborhood car alarms, some folks said the noise — which seemed like an explosion — could be felt.
One reader described the sound being "like a cannon" from her home by .
Another reader who was sitting on his patio on San Miguel Avenue describes the sound as that similiar to a dry ice bomb going off.
"When you put some dry ice in a plastic soda bottle, put some water in and close the cap, pressure builds and creates a loud boom [don't do this kids]" he posted on our Facebook page.
Sgt. JD Nelson of the Alameda County Sheriff's Office said the noise could possibly have been from someone setting off fireworks, but could not confirm this because they police were unable to trace the noise to a specific person or area.
A CVLegends Facebook reader had mentioned police activity on Marques Court near Lake Chabot. Nelson said this was due to reports by neighbors that a man was carrying what was believed to be a real gun. However, once police tracked him down, he was found with a BB gun. Nelson said the man was not arrested but added that the sounds people heard possibly could have been from gunshots fired.
This story will be updated as more information is made available.