AV audio question

I have Comcast cable. I take audio from the cable/DVR box via HDMI (only about 3 feet) to aging Harman Kardon AVR. In the last few weeks, the audio cuts in and out, but only on certain channels (like Turner Classic Movies, my favorite channel). Comcast has reset my box twice remotely, their default means of offering help, to no avail.

Thanks in advance for any suggestions.
If it is only on certain channels, then I would suspect that those channels don't support the 5.1 audio selection set on your AVR. Have you tried setting the AVR to dolby digital 2.0 and see if the droputs occur. I know on my DirecTv receiver some channels don't offer a very good 5.1 digital feed and the sound is more dolby pro logic than dolby digital.
When watching tv, are you seeing any pixeling ?

If you have their internet service, do you have slow browsing ?
sounds like you need a signal booster. My experience is it's better to get one from the installer/technician than to buy your own.
I do occasionally get pixeling. Does that suggest a weak signal?

Thanks, Theo, I'll try dolby pro logic
Does that suggest a weak signal?

It very well could be a low signal, but there could also be a loose fitting some place that could be causing your issues as well. A bad fitting any where from the tap to the tv could also be causing the problem.

If you would like more info, email me....and if not, I would set up a trouble call and have a tech come out and check the house for the things mentioned above and for noise.
Theo....thanks, the problem turned out to be dependent on which surround/dolby mode I used. Easy fix and now I'm off to read the manual!

Thanks to all who offered suggestions