can I auto-mute 'line' channel when not using tvtime?

[Andy Stone]

I use TVtime to watch telly, and the audio signal comes into my audigy 
soundcard via the line channel from a bttv card. All is well, apart from 
an annoying interferance noise from any screen activity when the telly 
is off but the line channel is still on.

I am a recent convert to Ubuntu from Gentoo (I love Ubuntu - big hats 
off to all contributors for putting together such a well made bit of kit 
- really world class. It has permanently replaced Gentoo for me, and I'm 
even growing to love Gnome!). Before I switched I used KdeTV and within 
it there was an option to have the line channel muted by default when 
not in use. On opening the telly app it would unmute and remute itself 
when I closed the telly again. This is exactly what I want to do here 
(TVtime, Gnome 2.8, alsa). I have searched documentation but not found a 
hint. Can you help me?

Thanks
Andy (n00b)

p.s. I have also just posted this on the forums.  Is this reasonable to 
do, to post the same question to both forums and this list?