Laptop DVD playback issues.

Got a HP Pavilion dv1000 laptop running Windows XP Home SP2 that has jitters in the audio when playing back a DVD. All other sound works fine, I’ve tried audio CD’s, avi and mpg files burnt to CD/DVD and they all work no problems, just when playing a DVD. I’ve re-installed codecs and drivers and the DVD burner has been replaced. If I plug an external DVD burner in via USB and play a DVD it works fine, its just the internal burner. Any ideas/suggestions?