Got any cordless phones by chance? I have a problem where C4 cuts out if I stand in certain positions in the room 50% of the time, or 100% of the time when I pick up the cordless. It goes pixelated, followed by the T100 rain fade message.
I finally have fibre! Had to leave the country to get it though.
I think there is a particular Sky set top box which is susceptible to interference from Dect phones.. either that or channels on a particular frequency.. can't remember which.. sure someone will remember more thab me :)