I'd be tempted to say rat(s), too, after my experience a number of years back. I had the pleasure if hearing faint scratching and tapping noises in our attic and presumed it was birds. A week or two later it was still going on but I also noticed that, a few minutes after it stopped, a burglar alarm would go off down the street. I spoke to a neighbour and he had even called the police because he had heard noises in his attic and then that burglar alarm sounding, which turned out to be a cafe further down the road. There was nothing to be seen in either of attics but the noise still continued so the council were called (free pest service) and they laid bait and traps. Three rats were caught (no idea how many got away) and then there was an environmental health check on the cafe, which was immediately closed!! Turned out that the rats were coming from a large nest in the attic of their property and crawling right the way along the whole row of terraced houses in the attic spaces.
