in my experiances plug wires breakdown over time, causing an increase in rf interference, so replaing them may help, as said before check your shielding on the coax

 

Dont know if its been answered yet, But Im a cb nut I have a nasty set up in my truck. Your problem will probably be cured by, making sure you 12v supply is direct to the battery and travels the shortest distance to the cb with out wrapping around other wires, also make sure there is the correct inline fuse. The ground need to be very short and direct to steal. Try and use 12g wire for both. The coaxial cable needs to be about 18ft and dont have it coiled up have is running around, (mine is in the headliner, my cb is mounted overhead) Dont ground out the antenna the mount will be the ground. try to mount the antenna in the middle of the bed behind the cab on the bed rail, best place to have teh least interference and the best ground plane.

Justin