Audio cuts off/skips when volume is at high levels

[PapaPrem]

I am having a problem where when I turn the volume up high while playing music on the Phatbox, the song will cut off for a second. It happens multiple times throughout the song. It doesn't happen when using the radio or cassette on my Head Unit. I can listen to the radio with the volume as high up as I want, without the audio cutting off. I tried many different MP3's. It happens to all of them. It doesn't happen when music is being played at normal volume levels.  Does anyone have any idea what the problem could be? I'm totally lost on this one.  By the way, I have a Volkswagen 2000 Passat (non-monsoon).