DDJ WeGO Soundcard Issue

I just got the DDJ-WEGO about a week ago and noticed that when I'm using the built in soundcard and running rca cables out to my speakers, the beat of the song seems to be slightly off. Almost as if the song is dragging and not hitting the 4/4 beat exactly in time. When I just use my computers built in output, the songs sound perfect. I am using Virtual DJ LE on Mac OS X 10.7.5 with 8GB of ram. I called Pioneer and they said to return it, so I did, and the problem is still happening. I also spoke with Virtual DJ and they said it has to be a problem with the soundcard on the WEGO. Any reason why this might be happening? Thanks.