High Frequency Hum/Buzz from HAI &SA UPB Light Switches


Hey friends, I've got over 50 HAI 35A00-1 Dimmer Switches that have developed an annoying hum at night. Oddly it doesn't happen all the time, but when it does you can hear this study high-frequency hum/buzz coming out of the switches. Definitely audible enough that you can hear it across the room.

Any idea on what could be going on or where I should look. They didn't always used to do this.
I have noticed this too, it’s always there (constant). It’s not the UPB commands because it’s a different buzzing sound.
It can get very annoying from time to time!
Mine isn't always there, some nights it is, some mornings it is… This persistent high pitch hum… Can't figure it out.