Found this at the Firestik antenna website:
Rolling Static
Compliments of Firestik® Antenna Company Technical Support Team
Copyright © 2007 Firestik® Antenna Company
Like leather-soled shoes crossing synthetic carpet in a low humidity environment, there are certain types of vehicle tires that are notorious for creating massive amounts of static electricity. You will know if your tires are the villain if your radio starts popping and crackling when you are moving down the highway but stops doing so when you come to a halt. This can be a real annoyance ... one that is more likely to occur when there is low humidity in the area, be it from winter freezing or summer dry spells in the southwest.
The only practical way to stop the problem is to give the static electricity some place to go ... otherwise your vehicle becomes an electrostatic generator and storage device. The best way that we know of is to attach a static strap to the vehicle chassis and let it drag on the road surface as you travel. Electrostatic discharge straps are generally made from a rubber material that has been cast or molded with non-sparking-type metallic particles such as copper, aluminum or brass. As you travel down the road the strap makes contact with the road surface and gives the electrical charge a place to discharge before it gets so strong that it discharges into the air and causes the popping and crackling in radio frequency (RF) devices.
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Since posting this page we have received many calls from people looking for a place to get anti-static straps. Apparently, it isn't so easy. We did some Internet research and found a couple of places. One offered straps that were a little gaudy [in our opinion] ... had a heart shaped reflector and some rhinestones on the strap. The other offered a more generic version for $19.95 that could be purchased on-line with PayPal or a credit card. The web site is Mizter.com
During the search we did note some other comments regarding the static straps. While our primary interest involved radio noise, there were mentions that spoke of eliminating dust build up on the vehicle. That makes sense [to us]. There was also many blog posts that talked about eliminating fatigue while driving long distances and as few from people who transport dogs to shows and they found that the incident of motion sickness declined (or went away) after the vehicle was outfitted with anti-static straps. While that information sounds a bit "out there" to us, we can not deny or confirm those claims."