Chris,
It gets sort of 'involved', but 'SwitchKit' is right, has to do with the way things are making contact, or not making contact. Unfortunately, that noise isn't ~only~ dealing with the radio and antenna(s), but with everything carrying electricity in/around the truck. Ever sit at the house listening and notice noise getting less (or higher) when it starts raining? That's usually the result of water/rain on power line contacts either cleaning the dirt off, or 'finishing' making the contact. Power companies fix that sort of thingy by replacing lines. (I seriously doubt if they ever just clean up and re-tighten connections or contacts, which would do the same thing.)
Since you can do very little about noise generated by the 'things' around your truck, you are sort of stuck with correcting things in/on your truck. (You were wondering what you could do in all that free time you have, weren't you?
) If it's loose or dirty, clean and tighten it. Everything, not just antennas, radios, power cords, rattling body panels, who knows what else. About the only thing you don't have to mess with is the pillow in the sleeper and the 'Monopoly' game!
After doing some of that for awhile, you'll be surprised at how much 'noise' you're willing to put up with.
'SwitchKit' is also right about those dual antennas, sort of. Depends a lot on exactly what you want to be able to do, but in most cases, they just aren't worth all the hassle. 'Simple' is good. I won't even try to get into which antenna is the 'best'! Most will work just fine as long as your expectations are reasonable. Personally, I couldn't care less about what the thing looks like if it works well, within reason, I'm 'partial' to pink ones...
- 'Doc
How do you know when you've done enough 'cleaning/tightening'? When you're to the point of ripping the @#$ radio out of the @#$ truck and seeing how far you can throw the @#$ thing.