I can't figure it out but my Cobalt is not showing up several MP3 files on my USB flash drive. I had recently copied these files but they pick up just fine on my PC. In the Cobalt, they don't show up.

 

It doesn't read ALL formats Tags and bit rates.

Some MP3's are just too complex for the player. I just use my aux input and phone for all music now mostly because the USB radio is a PIA , you never know what files it will play. you just hope as you drive off you will get to listen to a couple folders you uploaded

For best results I flash the drive to fat , slower speed but it usually handles the directories and such better on the radio in the car. In other words it aint perfect.