Try to tune to that Fox Channel again, and when the pixelization is happening or when you get the pixels hit menu>settings>system info on that screen you will see a "press info for more details" and that will give you an SNR value. That SNR value should be at the very least 32 and as hi as 42.
At and under 32, you will notice pixelization and even a loss of picture all together. If it's low, then yes - reseat your coax cables, retighten and clean them, and even think about replacing them if neccessary.
If it's just one TV that is having the problem then it's just the one cable you need to worry about.
