Is it Possible

There used to be lo-pass filters available at Radio Shack back in the 70's... A CB shop should know if a lo or hi pass filter would be best. They go in-line between the radio and the antenna, and don't screw up the SWR.

 

Back in the day, I used to install a filter on the power line of my higher power AM/FM cassette players and my amps. It effectivly got rid of all the noises over the radio that came fromt he alternator, fan motor etc.

I really don't think it is your antenna or coax, I think you are just encountering noise through the power line.

I get some noise in the truck over my CB and I have tried them clip on filters etc and nothing seems to help other then turning down the fan speed. It is actually worse when I run the fan in the bunk so I just leave that off unless I am sleeping. But then I am not using the radio anyway. LOL

One thing that had bugged me for along time was that my AM/FM/CD player would bleed over onto my CB and my CB would bleed over onto the AM/FM/CD. Meaning when I was listeining to music, the needle on my CB would bounce to the beat of the music and I could hear the beat over the CB. Never really did figure out why but it only happened in this truck and not the other trucks that I have run. I just turned off the music when I am playing on the CB.

 

That's what I would do first...Get a double shielded coax, something like LMR 240 or LMR 400...And if that doesn't take care of the problem, it maybe time to start doing some bonding on the truck by grounding body parts to the frame.