Noise in a ceiling is unnerving and almost impossible to place. But rodents keep fairly reliable hours, and what you hear and when is genuinely useful information, often enough to know roughly what you are dealing with before anyone goes into the roof space.
Just after dark, moving fast, along one line
Most likely roof rats travelling a habitual route. They are excellent climbers, they favour the upper parts of a building, and they run the same path nightly, which is why the sound seems to follow a line rather than wander. That repeated route is exactly what makes them treatable: bait and traps go on the run, not scattered about the loft.
Heavier, slower, lower down, often near the kitchen
More likely a Norway rat, which prefers ground level, drains and burrows. Hearing one above suggests it is getting up through a cavity or a service duct, and that route matters more than the animal.
Light, scurrying, several sources at once
Usually mice. They range far less than rats and there are almost always more of them than you think, nesting close to a food source and making many short trips rather than a few long ones.
What to look for in daylight
- Droppings, and whether they are shiny and soft or grey and crumbling, one means now, the other means a while ago.
- Rub marks: dark greasy smears where fur has repeatedly brushed a beam or a pipe.
- Gnawing on cable insulation, which is a fire risk and worth treating as urgent.
- Gaps where the roof meets the wall, round soil pipes, and under eaves. A young rat needs very little.
- Overhanging branches touching the roof, which are the commonest way up.
A word on poison bought over a counter
Loose bait laid in a roof space is a genuine hazard to children, pets and the birds that scavenge afterwards, and an animal that dies inside a cavity is a smell you will live with for weeks. Rodenticide belongs in a lockable, labelled station on a known run, placed by somebody who will come back and account for what has been taken.