Humming sound when applying brake pedal

This is called an ABS activation event. That means that the ABS is thinking that it needs to pulse the brakes due to some aggressive breaking situation. I attached the basic operation of the system. Most important thing is the signal inputs to the ABS that it looks at to determine if it is needed. I suspect you have an issue with the stop light switch. It may not be the sensor itself but I suspect the issue is with this input. Do you have a scan tool that we can look at the switch state and see what the pressure it is reading?