Well, I still do not have a good answer for you yet.
Do you have a Sound Blaster Audigy card? We have seen quite a few problems with this sound card.
Without regard to what sound card you have, updating the sound card driver sometimes solves the problems.
Also, please try this:
On TV Options Dialog, go to the "Advance Properties" tab. Double-click "Second Crossbar..." if it exists, otherwise double-click "Video Crossbar...". In the resulting dialog, select "Audio Decoder Out" from the drop-down list in the "Output" section, and check what appears in the drop-down list in the "Input" section. It should be "Audio Tuner In". If it is not, try setting it to "Audio Tuner In".
Another thing to look at:
Again in "Advanced Properties", double-click "Audio Capture Filter...". In the resulting dialog, make sure "Line-In" (or "CD Audio" or whichever channel your tuner's sound is connected to) is the one that is Enabled.