I'm getting this phenomenon in my M3. I'm using a standard 3.5mm to 3.5mm stereo jack cable and playing Pandora in my car. When any volume is applied at all, even if there's no signal coming from the iphone, I get a rather loud very high pitched tone that overlays the signal. When I turn the volume ALL the way down, it goes away. It also appears to be sensitive to the volume (gain) on the car's audio system. It's extremely annoying, and I never had this problem before with any other phone. Anyone experience this or know how to fix it? I'm wondering if it's some kind of weird ground loop issue on account of the metal iphone chassis. All my other phones have been largely plastic.