recording problem: volume not "even"

Hi

I've got line in hooked up to a TV tuner. Occasionally I'd like to record a
show, or just the audio part of it.

However, whenever I do that I get a recording that has massive volume
fluctuations. For a few seconds sound level may be fine, sometimes it drops
to a whisper for another few seconds, sometimes it gets overly loud - there
does not seem to be any rhyme or reason to it.

What I don't get there: Listening to line in sounds just fine. So it must be
something with the recording settings - but what...?

Heeeeelp

Thanks
J