Yes, rule out reception problems before moving on to the hardware diagnosis.
When you get pixelation or other picture defects, bring up the information plate ("i-plate") by pressing the i button on the handset. At the lower right of the i-plate there are two meters for signal strength (upper, orange) and quality (lower, green). What do they show? Strength could go down as low as three or four bars without it being a problem, but if it's high at ten bars the signal could be overloading the input. Quality needs to be ten bars.
However, the i-plate isn't the best way to assess signal quality. For a better determination go to Menu >> Settings >> System >> Signal Detection, then cursor right and choose your multiplex channels one by one. For each multiplex, monitor the live strength and quality readings and see if they bounce around or are steady, if steady what their readings are.
Note that the HDMI interface to the TV can radiate interfering signals that obliterate the TV aerial signal. To check whether this is the cause, start a programme recording and then after a few minutes turn the 'Fox to standby. A few minutes later again turn it back on. Run the recording and see whether the problems are recorded, and whether they are still recorded in standby. The results of this will tell us a great deal.
Presuming no signal problems can be found, the hard drive remains a suspect. Live programmes, even if not being recorded, are still dumped to the time shift buffer on disk, and if that particular partition (it is separate from normal recordings) runs into trouble the continual write retries overload the system and can result in picture faults.
