PSEG Power Connecticut on Tuesday explained what caused a booming sound Monday night in Bridgeport that was so loud that it prompted frightened residents to call 911.

The calls were regarding the sounds coming from the PSEG power plant in the city's South End.

Fire officials say they immediately responded to the plant and were met by staff members who said the noise was a controlled steam release. On Tuesday, a PSEG spokesperson clarified that the sound was not a controlled steam release, but a boiler leak.

Some residents say they should have been notified that the noise was not a safety issue. PSEG released a statement in which it says that were there any public danger, it would have alerted neighborhood residents.

A PSEG spokesperson says crews are investigating the cause of the leak and making repairs.