When I connect my Motorla Defy to the usb cable and connect that to my stereo in my car car, it plays fine for a while then just randomly shuts off. It happens multiple times in a day. Kinda frustrating when I use it in my car because I have all of my music on my phone. This is my 3rd defy in the last 6 months or so. The other two didn't have this issue. Any ideas what could be causing this.