I would suggest watching the TV via the Sony 970 integrated freeview receiver for a while.
You can then determine if the pixellated signal is on the reception side, or occurs only after the signal is recorded and played back.
My Sony 870 has both a signal level indicator and quality indicator for the freeview decoder and show something like 60% signal level and 100% quality for mainstream channels and I have far less breakups with this signal level than when using a Panasonic set-top box on the same aerial.
A problem I have with the 870 is that timed recording data using the EPG is lost overnight. I'm awaiting a reply from Sony hopefully to tell me what I'm doing wtong.