[Elecraft] External speaker hum with K3

[Greg Mason]

I connected a pair of Bose Companion 2 computer speakers (magentically shielded with amplifier) to my K3 and was rewared with a strong hum.  I have ensured that the speaker setting is correct and I am using the Bose stereo connector.  I also get the same result with the line out at various settings.The speakers work fine with my iPad and computer, so they are not the problem.  I finally connected them to the headphone jack and they work very well.  The right channel unit has a head phone jack, so I do not lose the muting functionality.  What am I missing with the connection to the speaker-out on the K3, which I would prefer to use?
 
Greg Mason
VE4AMN
masongregc43 at yahoo.ca