On at least 3 occasions now I have heard a scraping
scrabbling noise coming from the corner of the house
where the internal foul stack is.

It sounds like a bird or animal with claws, inside and trying
to get up the pipe, presumably because it can see daylight.

I'm pretty sure it is not inside the house.

I am on a spur of 9 houses connected to a 100mm run of
drainage and apart from the house at the head of the spur,
they are original properties with bird guards in situ.

If the neighbour hadn't covered her half of the shared
manhole connection I would lift and see if the poor
creature (probably a starling, they get everywhere)
could escape.