A report of an active shooter at Topsail High School sparked law enforcement response Friday morning, according to FOX 8 in North Carolina.
Collins said a popping sound from the heater "sounded just like an AR-15 (semiautomatic rifle) going off", the newspaper reported.
No shooter was found when a SWAT team swept the school, and the sound was instead determined to have come from a water heater with a faulty combustion chamber.
Several other schools in Pender County were placed on lockdown as a precaution.
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"Pender County Schools is thankful everyone is safe and thanks local emergency services for its immediate response", the school tweeted.
WECT reported that officers and deputies from the Topsail Police Department, the Pender County Sheriff's Office and UNC-Wilmington were at the scene, and the school campus was sealed off.
Williams said he has heard the sound personally and can understand how someone might hear it and make a report.
Numerous law enforcement officials were at the high school Friday morning.
School buses have been corralled at the Lowes Foods parking lot across from the school campus. Authorities said he claimed to have brought the gun to school because he planned to stop a rumored school shooter. According to its website, school begins at 8:30 a.m. It has around 1,300 students enrolled.