I have the same problem. The Becker radio has a separate battery
though. I have not tried ferrite cores.

What I found was I could stop the problem by applying inward pressure
on the power cable, but once I released the pressure it was back to
unsquelched radio. It stops also if I move the unit further away from
the radio. I cannot figure out why the problem is intermittent. I
would think it would constantly cause interference, but it comes and
goes.

I'd be interested to know if yours stops with pressure applied to the
plug.

I have not tried adjusting radio squelch settings as the radio is at
the bottom of the stack and the adjuster is buried within. And I
cannot force the problem to happen on the ground.

Bob