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.