I'm trying to figure out what's causing it or, at least, how to stop it
on that particular jack. Obviously, the intercom wiring runs adjacent to
the electrical buses on that side of the panel, so I'm not sure what
role the buses may play, especially since I'm using shielded cable.

Well, if it makes you feel any better, the co-pilot's jack in our
Pathfinder has a bit of whine in it, too. None of the other jacks do.

It's not bothersome, and I always figured it was the proximity to the
electrical bus.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"