Accordingly to the Beeb, it’s been kicking around since 2008. I wonder if, just possibly, there might have been a bug in certain contemporary gif renderers of that vintage that allowed video signals, in some obscure circumstances, to bleed through into audio channels?
I do remember, days of analogue TVs built with valve technology, it was quite hard to prevent some video, usually scene-dependent, from causing audio interference. But I don’t remember seeing many animated gifs in those days.