Audio Problems when encoding from DVD Player

I have the occasional need to encode video from a stand-alone DVD player. The audio runs through a mixer. When the composite output is routed through the mixer, the audio cuts out momentarily when the DVD is playing, resulting in a "popping" sound. This seems to be when the disc goes from one chapter to the next. And it only occurs when the audio is routed through the mixer and not when it's connected directly to a TV or monitor. And this only happens with an industrial DVD player - the Pioneer 7400. Doesn't happen with consumer models. The main difference with the audio bt the Pioneer & the consumer models is that the Pioneer has 5.1 surround sound. Could this have something to do with a surround sound setting?