I've had the Droid 4 vehicle navigation dock for a couple weeks and I've noticed that when using the included USB audio/power cable, my car speakers have a lot of static/distortion at louder parts of songs; I don't have that problem if I connect it via the 3.5mm jack.
I used to have the static problem with the 3.5mm jack as well but realized that if the phone media volume was set lower than around 70%, then it's fine. Unfortunately when the USB audio cable is used, the phone media volume settings don't change the volume and I have to use my car volume knob instead.
Anyone else having this problem? Is there a way to lower the volume from the phone itself when using the USB cable for audio? I'm guessing that's probably the culprit.