[CQ-Contest] SO2R filtering help

[Dan]

I am baffled by a problem that I’m having setting up to do interference free SO2R operating running LP. I’ve tried stubs and they have no effect on harmonics. I have good W3NQN style bandpass filters and THEY don’t seem to knock down harmonics. I know the stubs/filters are working as they greatly attenuate received signals if I put them on the band of harmonic attenuation. (40 meter filter in line while receiving on on 20 ) I’m using a K3 an FT1000MP. Filtering and stubs have no effect on either radio.

I have read that there could be something other than the rigs creating harmonics. IE  corrosion, wall warts, grounding problems. What I need are ideas on how to track these buggers if indeed this is the problem.
Thanks in advance 

Dan W8CAR