problem which sounds like 2nd order intermodulation

[ON5KQ]

Hi John,
I don't know, if it could have to do with the last update 1.223... perhaps - that's why I want to document this strange behaviour here:

Today I realized some weak (S5) phantom signals, on 18960khz which appears the double frequency of 9480kHz (31m band) - The original signal is about S9+45db on 9480kHz - sounds like typical IM2 problem from strong BC-signals on dead highbands... B U T !
The strange thing:
(1) no ADC clipping at the kiwi indicated
(2) additional external 10db attenuator (SMA type) doesn't make a difference
(3) if I unplug the antenna cable and plug it in my Elad FDM-S2 the phantom signal is not audible, even with full sensitivity from the ELAD..

What is the conclusion ?

It couldn't be IM2 problem because of (2)
It cannot be a BC-transmitter problem because of (3)
No ADC clipping - at least not shown by GUI
It couldn't be my own antenna problem here locally, because of (3)

What could be the problem ? Is my Kiwi broken ?!
Have you ever noted such phenomenon ?
I must have to do with strong signals - at least I haven't seen it with lower spectrum signals earlier.
Also it is hardly visible in the total spectrum so if you do not search dead bands in the evening zoomed in the spectrum you would never find it - but this evening I was searching for weak signals on closing highbands especially, because I made some changes to the antennas.

Is there anything I can do or test with the Kiwi, so I know it works normally or not ?

Many thanks and best regards,
Ulli, ON5KQ