Problem
Sometimes, recorded TV shows have no sound. This is of course very annoying because the recorded show is worthless.
Also, when switching channels while watching live TV, sometimes a channel has no sound. This is always solved by switching channel again and then back (most often, once will do the trick). Media Center doesn't do this trick by itself when recording of course, so that's the bigger issue - but the cause is certainly the same.

Details

• The computer is running a newly installed Windows 7 and Windows Media Center.
• It has 2 different tuner-cards installed. Both are installed with signed and up-to-date Win7 drivers and appear OK in Device Manager.
• Both tuners get the same antenna signal, from a split cable from the wall. The cable delivers analog cable TV (40+ channels) and digital cable TV (4 channels) at the same time.
• Both tuners have been configured to receive both analog and digital channels.
• This only happens with analog channels.

How can I fix the no-sound problem?

Update:
I've now spent some time with the computer to try and pinpoint the problem, but I've had little success so far:

• I flipped through the channels until one didn't have sound, then I disconnected the antenna cable from one of the tuners. It was the right one because then the video also went away.
• I flipped lots more channels to see if the other card also would come up mute once but I never had a channel without sound. It might still be possible, I don't know.
• Then I disconnected the "good" tuner and connected the "bad" tuner and again flipped lots of channels but again I never had a channel without sound.
• It seems to me that the problem is erratic. It happens on any channel, and I haven't ruled out yet that it only happens on one tuner.