Let me make sure I understand correctly. You made a disk on the Liteon 5004/5005. This same disk plays back correctly on your PC. But the audio "breaks up" when played on either Liteon machine.
Do any disks (commercial DVDs for example) playback with proper audio on your Liteon? If they don't, then the issue cannot be on the recording side of things. I suspect it isn't anyway or else why would they playback OK on the PC.
Do you have your Liteon connected to a home theater or stereo system? If so, have you double checked the connections to make sure it is not a faulty cable? If connected to a home theater or stereo system, try playing back through the TV speakers instead. Or as an alternative, try playing an audio CD in your 5005 and see if it sounds OK.
It would be strange, but not impossible to get two different units with the same problem. That's why I suspect something outside the Liteon as the culprit.
Post back with additional information and let's see if we can't narrow this down more.