Loosing voices on recordings?

Over the past few weeks I have been loosing the voices on a few recorded shows. It only happens from a CBS show. And only from a recorded show, never from live tv. All the background noise of the scene is still playing but the voices drop out for a few seconds and then eventually come back. I have 2 HDDVR's that this happens with. The HR20-700 gets it's network feeds from the antenna then through the DVR. The HR22-100 gets it's network feed from the sat. Again it only happens on a CBS show and it doesn't happen to the same show all the time. Been watching it now for a few weeks trying to see if there is some type of pattern and I can't find one yet except for CBS and recordings. Both HDDVR's go from Sat. receiver to A/V receiver via HDMI cable then to surround speakers. Haven't had the problem with any other channels and/or recordings. Any one have any ideas would be greatly appreciated, thank you.