The answer to 'why is my GFCI outlet sparking' is that a sparking GFCI outlet is usually a sign of an electrical problem that requires immediate attention. GFCI outlets are designed to trip and cut power when they detect a ground fault, which is an unintended electrical path. Sparking indicates the GFCI is functioning as intended to prevent electrical shock, but the underlying issue needs to be addressed.
Common causes of a sparking GFCI outlet include a short circuit, damaged wiring, or a malfunctioning GFCI. It's important not to reset the GFCI repeatedly if it keeps tripping, as that can be a fire hazard. Instead, you should unplug any devices, reset the GFCI, and if it trips again, you'll need to call an electrician to diagnose and fix the problem.