Corrupted sound from DVD players

[Wizman]

I have 2 DVD players on my PC - a Lite-On DVDRW LH-18A 1H and a Sony DVDRW DW-D22A. Until recently they both worked perfectly. Now, for a reason I can't identify they both play DVDs and CDs with slightly corrupted sound - the sound is crackly, occasionally slightly slow and occasionally 'warbly'. Both players are affected. The discs themselves play perfectly well on other devices, and music and video that is on the hard drive plays perfectly well. I have ripped a chapter of a DVD to the hard drive to see how that works, and that plays perfectly well from the hard drive despite having been ripped from the 'faulty' DVD players. Music DVDs have background music on the menu chapters of the DVD - this background music is only heard if I play the DVD with Power DVD. If I play with any other software that background music is not played. A couple of DVDs that are not music don't play any sound at all unless I use Power DVD. Even using Power DVD the sound is of poor quality. The DVDs can be listened to - the quality isn't appalling, but something is wrong, and I don't like it.

I am running XP with SP2. I'm not sure what my soundcard is - sorry - though it might be AVerMedia DVB-T WDM - does that sound like a soundcard? 3 GHz P3, 1 GB RAM

Any clues would be good!

Thanks