When I stream audio from my iPhone 4 into my Ford Sync audio system over bluetooth, the audio quality is excellent. However, if I plug in a USB cable to get access to the hands-free features, then the audio quality degrades almost immediately. Sound comes out with "hissing" sounds, pops and cracks. This is even more noticeable when listening to spoken word or podcasts.
I have tried different USB cables and have verified that the same audio files do not play with the same defects thru the iPhone's speakers when using headphones. Also, the same files played over my Mac sound just fine. Any pointers would be appreciated. If you are experiencing this same problem with your Ford Sync system, please add a comment to know that at least I am not the only one experiencing this issue. Thanks.