Vision but no sound - why?

Hi
I have been trying to copy a retail dvd and no matter what I put it
through -
AnyDVD, DVDFab Decrypter, dvd shrink, dvd Decrypter, ripit4me
and then Nero 8 on Vista, I can get picture but only sometimes a
muffled sound.

I haven't had this prob before and I'm beginning to think the dvd is
at fault, but I can't return it saying It won't copy !!

Would anyone have any idea what is wrong and know if there is a fix or
work around please?
--
Martin
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