Notifier AMG-1 Humming Noise

I have my Notifier AMG-1 wired and programmed to my CPU2-640 everything works fine but I have a constant low pitch hum coming from the fire alarm speaker. Any thoughts on how I can fix this?

May have to adjust the pre-amp gain.
On the older panels, if set too high, it would cause a problem with the handset module.
Try adjusting and listen to the results.