Audio "Hum" from XLR Booth and Master RCA

I have had my DJM S9 for 2 + years with no issues.  However, yesterday I started getting a "hum" from the master RCA and the Booth XLR.  The hum is not not stop.  It will drop off for a while and then come back on for no apparent reason.  The hum continues when I turn the power off on the unit, BUT it stops when i disconnect the power cord.  I've tried connecting the unit to another wall outlet using different power cords and I still get the humming.  

Set up

Windows 10 64 bit

Firmware DJM s9 1.08

Driver - current as of 2/23

Software: Serato Pro DJ and Virtual DJ (not at the same time)

Hum is audible even not using either software packets

Can anyone assist with this issue?