We've got something up in the loft. a few droppings - about the size of sunflower seeds - so not mice, is it likely to be squirrels. Can't imagine a rat shinning up a drainpipe. No signs of anything chewed or gnawed so far. so I guess next stop is putting down some traps?
Rats definitely. And they get into roofs. We have problems most years (we live rurally near a farm and rats will always be a problem). You would be surprised how easy is is for rats to climb up walls, they are very clever little blighters.