N-Jin

When I'm using the mp3 minim ack input, it will play with decent volume for about 1-2 seconds, then the sound is gone, and I only hear some signal if I push the gain up to max on my apogee duet. I have to listen to the music through the instrument input. This way it's impossible to both use it as a bass amp and playing mp3s at the same time. What do I do? I believe nothing else is wrong with it. I'm wondering if it's kind of a "software" issue? Thanks in advance!