Interference with iPhone car charger.

The iPhone is not shielded, hence it will cause interference with other electrical equipment, especially if it is near your stereo (as it is in all cars). Try putting the phone into airplane mode and see if that takes care of the issue.

If not, as far as I know, the PowerJolt by Griffin, sold at the Apple Stores, is the only approved car charger as far as I have seen.

I have the same problem, nguerrera. I connect to my car stereo via a stereo mini cable (I think that's what you mean, not RCA, which the iPhone doesn't have a jack for) and I've tried two non-USB Griffin car chargers. They both make a terrible buzzing noise when both a plugged into the car. I was thinking it was the charger, but now I'm beginning to believe that i can't have both connected at the same time.

I also have this problem.

I was also having problems with noise when I had an adapter for my iPhone 3G plugged in to the cigarette lighter socket in the car and playing music through a cable going into the AUX connector of my car stereo. After having trouble with one, I went and bought a Griffin PowerJolt SE but still had a noise problem. After doing some tweeking, I fixed my problem.
1) It makes no difference whether the airplane mode is on or off, because the interference isn't coming from there.
2) The amount of noise varies depending upon whether your car engine is running or the ignition switch is in the accessories position. There will likely be a high pitched whine in the latter but also a clicking noise in the first mode. This is interference from the spark plugs in the car. This noise will also vary depending upon the speed of the engine. Also the noise will go away when you are not plugged into the charger.
3) Check two things in the settings in your iPhone. First, check that the volume limit on the phone is off or is set fairly high.
4) Now check the volume setting on your iPhone. This needs to be at or near the maximum.

If the last two conditions are not true, then what is happening is that the noise that is coming in through the iPhone from the car ignition and the charger is too loud compared to the audio. This then causes the car amplifier to amplify both the noise and the music for you to hear anything. When the iPhone volume is higher compared to the noise, then the car amplifier amplifies the audio less, but it also amplifies the noise less.

At least these changes made a big difference on my iPhone.

Mark S. Harris
An Electronics, but not an Audio Engineer