TiVo audio/video "glitch" on just 1 channel

Did this just start or is this a new TiVo, or what changed recently?

What model is the other TiVo? What are the signal strength, SNR and RS Error counts on this channel for both boxes, from DVR Diagnostics.

Try swapping the locations of the two TiVo's. Does the problem stick to the box or to the location?

Started recently on my 3 year old TiVoHD. The second TiVo is a Premiere connected on the same cable feed. No recent changes. Both have CCs and are fed from the same wall outlet via a splitter. Both are supplied through a VR UPS.
I just ran through setup again, hoping I could disable the CC to eliminate that from the equation, but the TiVo wouldn't let me ignore the CC. I considered removing it temporarily, and doing a full setup to see if it made any difference, but the CSR at Comcast dissuaded me from that, saying it would take a truck roll to get the CC working again. Not sure if that's a fact or just "good salesmanship" on the part of the CSR.
After running through seup again, however, I recorded two shows on the offending channel and did not yet hear the audio glitch. I have it set to record this evening in the time slot where it occurs repeatedly, but as it's the weekend, it will not be the same show.
I'll add to this if I learn anything new.
Thanks!