This can happen with some movies depending on how the sound was mixed originally. More specifically, many TV movies made for Crown Media in the mid to late 2000s have a large musical component. The producers believed that the addition of music, even when dialog is present, enhanced the presentation. However, hindsight has proven that this makes the dialog difficult for some people to understand.
We also want to remind people that our content does not stream in Dolby 5.1 surround sound, so trying to play our stereo sound in higher quality may result in a similar sort of audio distortion.