This sounds like an EDID problem. It can happen when the audio format from the source changes like DSP81 mentioned. Since you are an Ethereal dealer just call Brent. Show the client that it is a Comcast issue by swapping the HDMI cable on the cable box with the one on the Blu ray. If the Blu ray works fine then that proves it is the cable box and not your system. I have found this helps justify the cost to the client for whatever HDMI repair piece you need.