I assume the sound output of your tv card goes through line in. Try KMix to deselect line in.
I love the new Knoppix DVD but have a problem I haven't encountered with any other distro of Linux - previous Knoppix included:
I have an old ATI TV Card in my computer and when my machine boots with Knoppix, it "senses" the card and immediate begins playing TV sound. If I try to load the TV software xawtv, the software works flawlessly - as good as the MS software that was made for the card. However, if I close the program, the sound stays on until I turn off the machine.
Of course I could mute it, but finding out how to fix the problem is so much more fun.
I assume the sound output of your tv card goes through line in. Try KMix to deselect line in.

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