Static in KX-165A

I have two KX-165A nav/coms in my Cessna 320F and static can be heard
through the headsets from both of these radios. The static is not
noticeable while flying, but can be heard during taxi. It can also be
heard with both engines off and all circuit breakers pulled except the
radio circuit breakers. If I turn off the KMA-28 the static is much
quieter, but still present. I've tried different headsets and plugging
into a different intercom jack, but still the static is there. If I turn
the radios off, then the static is gone, so it is coming from the radios.
Is there an adjustment on the KX-165A's that could get rid of this static?