I have just upgraded from a previous Dune to Dune HD Real Vision. I keep my video files on external hard drives and plug in using the USB port. However, sometimes when I play a file, Dune says that there is no recognisable audio. If I do a Factory Reset, it then recognises the audio and plays it back with no problem. This has happened a couple of times. Can anyone give me some advice on how to stop this from happening? Thanks.