In article . com,
"mikem" wrote:

Jonathan,

read this
http://tinyurl.com/l4rkk


Mike,

That's very helpful, but unless I'm missing something, I'm not sure that
it explains why I'm only having the whine problem on the right side of
the cabin (in both front and rear jacks). All jacks are isolated from
the airframe, and I'm running a common ground back to the intercom
ground. The braided shield is floating at the jack ends and grounded at
the intercom ground point. The whine on one side of the cabin would
make more sense to me if the jacks were grounded locally to the
airframe, but not sure how noise would enter (or exit) the system on one
side of the cabin with the intercom system on a single-point ground.

Outside of the stuff I've posted to the newsgroup, one other oddity:
when I activate the marker beacon output on the audio panel, the whine
is more noticeable.

Obviously, it sounds like there's a ground problem somewhere, but I
don't know where to start. I'm baffled as to why I'm only hearing the
problem on one side of the intercom system and not the other, with none
of the jacks or PTT switches grounded directly to the airframe. The
noise must be alternator-induced, because it is only present when the
alternator field is activated. If something was looping through the
audio panel or somewhere else, why would it only affect the jacks on one
side of the aircraft?



JKG