Rick:

There is nothing surprising about what you describe. That is how
harmonic interference is likely to play out. Let's say for instance
that the MRX has a 9.5 Mhz microprocessor clock; the 13th harmonic of
that would be 123.50 Mhz. But microprocessor oscillators don't need
to be perfectly precise. If yours happens to be low by 0.2% then
yours falls on 123.30 and someone else will find interference on
another nearby frequency or not at all if the 13th harmonic happens to
land right between radio channels or on a frequency that pilot B never
tunes in. I have an MRX with sloppy external power connections and
have never had interference; so maybe I am the pilot B case. Of
course, I don't really know what clock freqencies are actually used in
the MRX and I don't know which harmonic is the nasty in this case --
my numbers are just for illustration.

Bob:

The business of pushing on the connector is most likely that your
fingers are capacitively coupling into the spurious radio propogation
path between the MRX and radio. The propogation path is shunted or in
some manner altered enough to make a big difference in the
interference that you are hearing. I'll bet that if you just squeezed
the connector without pushing you would find the same effect.

Steve Koerner
(retired EE)