Thanks to all. I'm going to try one of these approaches and see.

Darrel Toepfer wrote:
mikem wrote:

The prob I've had with the audio is a loud buzz unless I unplug the
power and run on battery.


Folks on Cessna Plots forum have had good luck with this:
http://www.crutchfield.com/S-xGL4Bin...35&i=127SNI135

and also a similar device available from RatShack


Radio Shacks is cheaper but requires adapters:
http://www.radioshack.com/product/in...entPage=family

Ground Loop Isolator $16.99 Model: 270-054

You'll need 2 (depends what you're adapting to) - RCA Female to Mini
Stereo Male adapters Catalog #: 274-883 $5.99 ea.
http://www.radioshack.com/product/in...entPage=family


Cheaper here ($2.38 each):
http://www.valcoelectronics.com/Merc..._Code =18-008


ES-034 The ES-034 isolates multiple components to prevent ground loops.
It may be used as a trouble-shooting installation tool, to break grounds
without removing grounding parts. The ES-034 is designed to interface
with line-level outputs and is equipped with two male and female RCA
jacks, for interconnection with cable adapters/components. $14.00
http://www.buyreliant.com/caudio/noise.htm
http://www.valcoelectronics.com/Merc...t_Code =ES034


So you'll need one of these (Stereo mini to dual RCA male $3.58):
http://www.valcoelectronics.com/Merc...ct_Code =Y3AA