I called TiVo Customer support. They said that the most likely cause was too strong a signal from the cable box and they recommended buying a "cable signal strength attenuator." Radio Shack staff seemed never to have heard of one and I was unable locate anything suitable on the web. I called TiVo again and asked for a specific part number so I could buy one. TiVo said it was "policy" not to recommend any specific part; they told me to call my cable provider (Verizon). Verizon never heard of such a thing. I called TiVo again, via Chat. Nothing they can do, said they. Has anyone else heard of a similar bizarre story?