[Elecraft] Phantom signals

[N4ZR]

I recently started using N1MM+'s spectrum display with my K3, and it 
made me notice that I have some phantom signals on the display. 
Specifically, there are steady carriers at 14039.6 and 28039.6. Each of 
these carriers has "sidebands" spaced 1 KHZ apart on either side. There 
is a slight AC roughness to the tones as heard in CW mode, particularly 
on 20M.  On 7039.6 and 21039.6 a single carrier is audible, much weaker 
than on 20 or 10 meters.

Disconnecting the antenna from the K3 does not affect these signals, nor 
does disconnecting my Airspy HF+ from the IF Out jack.

Any idea what these might be?  Because they are discrete frequencies and 
relatively weak, they aren't particularly an operational problem, but

73, Pete N4ZR
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