Here is a simple test for you. Put your multimeter in VAC mode and measure the rms voltage across the terminals at the refrigerator
. This will tell you if you have a noise
problem or ac voltage on the dc leads. Unlikely, but possible. A battery
is a huge capacitor and filters out most noise
. If the cable run from the battery
to the charger is long then the filtering of the batteries is reduced. Here is the kicker
for you. Your model frig is an AC unit with a built in inverter
to supply the AC. It is not really a dc unit at all. There maybe a harmonic or switching frequency problem between the frig and the charger circuits. Again, unlikely but possible, easily fixed.
A method is to add a large capacitor directly at the xantrex connection (across the + and -). These are available at Radio
Shack, most audio stores. Rating of at least 24v. I would use about .5 farad, no larger. You may have one of these in your car audio system. Another test for this is to move the charger very close (short leads) to the battery. Maybe within a foot or two.