bad ground ?

The radio is grounded via the power cable and, should be strait to the battery pos and neg.

 

Putting a ground strap from the rig to frame may help, but your rig may well already have that from the mounting bracket.

Since the problem is getting worse, my guess is that the door is losing its bonding to the frame. If you don't have a bonding strap between the door and the door frame, you are using the hinges to provide that bonding. As hinges wear, they don't do that so well.

 

high SWRs will cause a significant drop in reception as well. line noise is line noise. have the SWRs been checked recently?

 

Not necessarily. Many of these antennas are designed to give low SWR when used against a poor ground. I've seen cases where improving the ground caused the SWR to go up.

 

Haven't heard that before. Which antennas would these be?

 

Things were bouncing and rubbing together producing a better ground?

 

There is some metal in the over hang that you can ground too if you want. You don't really need a strap for such a short run to ground. I have used 10 guage wire for short runs like this and it has worked just fine. I would look more at chassis grounds though and also check to make sure that coroation has nto made its way into your antenna bracket. I have had it build up in the empty space inside the plastic washer and actually short out the antenna. Take the antenna mount apart and clean everything up. If you see white crap in there then that may be causing issues. You want good clean shiney everything.