Hum on multiple DJM S9

Hi,

I have been touring hard with the DJM S9 since it came out. I'm now onto my 4th. They have all developed the same fault after about 1.5-2 years of service. They get a hum through the XLR balanced outputs that occurs whenever an active power cable is put in.

The unit can be off, and it will still hum. I've had the licensed pioneer repair guy here in Sydney Australia try to fix, but even replacing the main board and power supply doesn't seem to fix it for long.

This hum is only audible at extreme volumes, but that's the kind of volumes that I work at and the mixer has been rejected by sound crews at major festivals. 

I made a video demonstrating the hum here:

https://www.dropbox.com/s/93g13acew7zmf4p/S9%20MIXER%20HUM.mp4?dl=0

I was excited to finally isolate and demonstrate this issue and thought you'd be interested and maybe offer some advice to me and my repair man on how to fix it.

Thanks