We too have seen the disappearing sound issue, though rarely.

I had occasional garbled video until I added a signal booster to the aeriel line.

On (rare) occasion we have a short total loss of sound, and slight video glitches, though this only seems to affect CTV8. I had one case of an entire recording from One being soundless, I didn't try to transfer it though. I have assumed this is because the TiVo needs a very strong signal and ours (even with booster) is insufficient.

We also have an occasional problem where when we switch the TV on, it cannot detect the HDMI signal from the TiVo. A quick power cycle of the TV fixes it, though.