Zaon MRX causing radio interference 2

I'm starting a new thread on this topic as the old one sort of drifted
off-topic and its conclusions don't seem to reflect what I've found...

I have a Zaon MRX which is *using external ship's power* which is
causing radio interference. I know it's the Zaon because when the
radio goes to static, in flight, as if the squelch wasn't adjusted,
turning off the Zaon immediately stops the problem.

Following the recommendations of this forum, I've installed one, then
two, then three ferrite cores on the Zaon end of the power cord. Each
additional core has reduced the number of static problems I've had,
but not to zero (and not to where I don't have to frequently turn the
damned thing off!).

Calling Zaon tech support today (800-496-9430 x-311/312), they say
they have a particular problem with sailplanes -- something about our
radios being particulary sensitive because they're low power compared
to a larger, standard GA unit on a power plane.

As such, they don't have any real solutions for running with external
power. He did suggest either a) trying more ferrite cores on the
Zaon power lead (!), b) trying a ferrite core on the negative (?) side
of the radio's power lead, or for the sure fix c) running the Zaon off
its internal battery or a *separate* external battery other than the
one driving the radio.

Anybody have any other suggestions?

Eric