Radio Ground - Static

[pastaben]

I have a 99 Venture I purchased in 2004. It was great, and generally still is. However, lately, I am noticing that my radio, especially in AM, picks up interference a lot more than it used to. I have the windshield antenna.

If I go on a steel bridge, I have a very loud, high pitched squelch. Its so bad I have to turn it off. When I go in a tunnel, the signal is very weak, but I get some reception. When I go under power transmission lines, its as if my stereo is going to blow up. If I drive along above ground power lines, I have a loud buzz along with the radio transmission. It was not doing this when I first bought the car. I also have another van, Chrysler, that is oblivious to power lines or bridges or tunnels.

Does anyone know if its just an increase in the powerlines around town, or, if there's a ground that I need to check or clean on my venture. Where is the ground for the radio?

Any help is appreciated. Thanks.