iPhone 4 improves on audio output isolation

I often hook up my iPhone to my car stereo and listen to podcasts while driving. I tend to drive with one earphone in place so I can click to pause or answer phone calls. In the past, whenever I turned off my car's stereo, I could still hear a indistinct and annoying noise coming through my headphones even though the sound was supposed to be going out the line level output in the phone's dock connector. Now, with the iPhone 4, it's quiet. Just another little improvement.