In article ,
Tauno Voipio wrote:
It still has the smell of a ground loop if the intercom
power supply filtering is OK.

Maybe a ground loop between the intercom and the radios
(audio panel)?


My wife is summoning, but some quick additional info:

1--When the alt. side of the master is switched off, the noise
disappears completely.

2--The noise is equally noticeable in the right FRONT and right REAR.
It is not noticeable in the left FRONT and left REAR.

3--Gets slightly worse as electrical load is added.

4--Sidetone from the radios is not as loud from the copilot position.

5--There is occasional popping when the mic is keyed from the copilot
position (but never from the pilot position.) The popping seems most
frequent when the engine is advanced to move onto the runway for takeoff
(during which time the mic is often keyed to announce takeoff.) This
electrical popping noise is never heard from the pilot position, and may
or may not reappear for the copilot when operating the mic in flight.


Thanks
JKG