I have a Cobra 19 DX IV wired directly to the battery and a Little Wil magnet mount antenna on the rear trunklid. I notice if the ignition is off and I turn the radio on, I get a steady drone sound. If I turn the car on, the drone now is slightly higher pitched and slightly louder. The drone does not change much when I'm driving around. It does not go up and down with the throttle. When someone's voice comes through the drone is eliminated. I am trying to figure out what the source of the noise is and what I have to do to eliminate it completely. What should I check? I looked where I wired the red and black wires to the battery and they look OK. I simply bent the wire into a hook shape and tightened the bolt around it so it is secured. Someone said to check the antenna cable - but I don't know how this could be a problem because I ran it under the steering wheel and down the drivers side between the plastic molding that makes the floorboards and the carpet. It then goes under the back seat into the trunk. Ahhh
Do I need to purchase a filter/cleaner, and which one should I get?