Does it smell, like arcing may be occuring? Is it hot to the touch, or warm for that matter? If so, there is definately a problem inside the device.
Occasionally, internal parts may shake loose, allowing them to be subject to the 60 cycle hum we have become familiar with through florescent lights and the like.
It may not be field serviceable, so, if it does not smell or feel hot, you may have to put up with it, or move it around, try to re-position it so it does not hum. In all seriousness, if it was mine, I would get it open, or replace it, you really do not want to fool around with electrical stuff that is not working at 100%. They may be expensive to replace, but not as expensive if it completely fails, and causes a fire....
Back to a 5'er after 4 yrs fulltime.
Pulling with a '14 2500 ram, 6.4 Hemi.
Montana High Country 31RE