There are a few different things that can cause an electrical humming noise. One possibility is that there is a loose connection somewhere in your electrical system. This can happen if a wire becomes loose or if a circuit breaker isn't properly connected. Another possibility is that there is a problem with your electrical panel. This could be caused by a loose screw or by something more serious, like a faulty breaker. If you're not sure what's causing the noise, it's best to call an electrician to take a look.