If you've rebooted your box, then pixellating pictures are symptomatic of a poor TV signal - this will be a fault somewhere.
A box being old shouldn't, of itself, cause this fault - I can see you've posted in the broadband section reporting some possible speed issues.. it may be that the 2 issues are both indicative of cabling problems, or they could be entirely separate and independent.
I would persist with calling through to TV faults - it may just be that if you have a fault on the incoming cabling, the automated system could run diagnostics that pick this up and offer an engineer visit without needing to call. The regulars in the broadband section may also be able to pull some stats from your SuperHub that might just identify something.
I would have also suggested looking at a box-swap to a V6 if you've had your TiVo for a while, but if there are signal issues on your cabling, then this would prevent a QuickStart install and you're likely to need an engineer visit in any case.
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