My 2013 Prius V 2 has a USB port next to the 12V power. In the past, I inserted a USB drive in the outlet, changed the source on the radio to USB and played my music or a book. Now I insert the USB (and the indicator light on the USB drive lights up so I know there is power) but when I attempt to change the source to USB it is greyed out. My source choices have become AM, FM, BT. I can't find anything on this in the manual.