The answer to 'GFCI outlet buzzing noise' is that a buzzing or humming sound from a GFCI (ground fault circuit interrupter) outlet is usually caused by an electrical issue. This could be due to a problem with the GFCI itself, wiring issues, or other electrical components in the circuit.
Some common causes include faulty GFCI components, loose wiring connections, or a ground fault in the circuit. The buzzing noise may also be accompanied by the GFCI tripping or not resetting properly. If the buzzing persists, it's best to have a qualified electrician inspect the outlet and electrical system to diagnose and resolve the issue.