[TenTec] ARGONAUT V Mobile Power Source

[Stuart Rohre]

There have been successful ferrite filters placed on each lead leaving a 
gas tank, if you can access the wiring right above the tank without 
dropping the tank.  If that is the suspected source of the noise, you 
can test for that fact, by turning on the key, but not starting the 
engine.  In many vehicles this starts the fuel pump in the tank, to 
pressurize the line, and the noise will appear if from that pump.

Worth a try.
-Stuart
K5KVH