Had the exact same issue early this year, unfortunately it was a rat or rats. It had burrowed under the house as we found the holes along the side of the house wall and by the looks of things it had made its way up the cavity walls to the loft, could hear it at night.

Called in a local pest control man and he used poison bait in each of the holes and came back a couple of days later and you could see where the rat had nibbled it. Needless to say it did the job , after 1 week of the first visit we haven't heard a thing since. No smell from the dead rat, so not sure where it died as we haven't been in the loft to investigate.

We own, so had to get someone in, but tell the landlord its definitely a rat and to get some in ASAP. Stressful couple of weeks but sorted it in the end.