Plextor PX-708A reading problem

I have the plextor PX-708A DVD writer and when I play a commercial DVD movie in for playback, every 20 seconds or so the DVD player pauses slightly and the sound stops as well. This cycle continues for the entire movie. I am playing it using Intervideo Windvd 5. I also tried Win DVD version 6. I am using a Creative labs audigy card. Computer is 2.4 ghz. I have installed the latest firm update. It seems to be happening only when switching sound to 5.1 surround sound in WinDVD. The movie plays fine if I choose stereo. Also, if I play the movie on my Pioneer DVD Rom it plays fine. Any ideas what this could be?

Have you checked if DMA is enabled for your drive? Experienced any other problems with your drive that could indicate a problem?