Originally Posted by Air Randy
Or, the motor in your fridge that runs the compressor could just be bad i.e. a brush has a slightly too large gap to the armature and is sparking. Or there is an inadequate or loose ground inside the fridge chassis.
If you know someone that has the same fridge as you do, try plugging their's into your rig in the same configuration as yours. If the noise goes away, its the fridge. If it stays, it is somewhere in the eletrical system of your truck.
Doh. why didn't I think of that!?? Oh Perrrrry..where are you?