[Elecraft] K3, Microham MK2R+, Rear Phone Jack = Hum

[Richard Thorne]

Hello Group,

I just installed a Microham MK2R+ SO2R box, I connected the HP Audio 
input of the MK2R+ to the 'rear' phone jack of the K3.

Lot's of hum on the receive audio and distortion on my monitored ssb 
transmissions.

When I unplugged the cable from the rear phone jack on the K3 and 
plugged it into the front panel phone jack, the hum goes away.

Any ideas why the front panel phone jack works without hum but the rear 
phone jack has hum?

I was hoping the rear jack would work as then I would have a totally 
uncluttered front panel on the K3, all the cables would be plugged in 
the rear.

Any ideas?

Thanks

Rich - N5ZC