In San Diego, scratching, running or gnawing in the ceiling after dark is most often roof rats in the attic. Light, quick scratching or rustling inside a wall is more often mice. The county says rats are most active at night, which is why the noise starts in the evening and fades by morning.
The kind of sound, when it happens and where it comes from usually tell you which rodent you have, and sometimes that it is not a rodent at all.
Sounds roof rats make
Roof rats are heavier than mice, and you can hear it.
- Running or galloping across the ceiling, often in a line from one side to the other
- Thumps when they jump down from a beam or a duct
- Gnawing: a steady scraping or grinding, sometimes for minutes at a time
- Scratching at the eaves or inside the wall near the roofline
- Squeaks or chattering, especially when several rats are in the attic
The sounds often start soon after dark and peak again in the hours before dawn. If you hear them near the outside walls more than the middle of the house, that fits rats moving along the top plates from an entry point at the eaves. See rats in the attic.
Sounds mice make
- Light, fast scratching or skittering
- Rustling in a wall or behind a cabinet
- Faint squeaks
- Small gnawing sounds inside walls or cabinets
Mice tend to stay close to food, so their sounds are often near the kitchen, pantry or laundry. If the sound moves up and down inside a wall, mice may be using the wall as a route between the attic or crawl space and the kitchen. See mice in the walls.
Other sounds that get mistaken for rodents
Not every night noise is a rodent.
- Ticking or popping as pipes, ducts and roof framing cool after a hot day, which is common in inland neighborhoods
- The AC or heat pump cycling and ducts expanding
- Birds nesting under roof tiles, which are usually loudest at dawn and dusk
- Raccoons or opossums, which are much heavier and thump rather than scurry
- Squirrels, which are active in the daytime, not at night
Rodent sounds move around and stop and start. House sounds tend to repeat in the same spot at the same time.
Where the sound comes from
Listen for a few nights and note:
- Ceiling over the whole house: rats in the attic
- Ceiling near an outside wall: rats coming in at the eaves
- Inside a wall, moving up and down: a route between attic and floor
- Inside a kitchen or bathroom wall: mice following plumbing
- Under the floor in an older raised-floor home: rodents in the crawl space
- Garage ceiling or rafters: rats nesting in stored items
That map tells you where to look for droppings and where traps should go first.
Confirm it with evidence
Sounds tell you something is there. Droppings, rub marks and gnawing tell you what. Check the attic through the hatch with a flashlight. Look under sinks and behind the stove. In the garage, look along walls and on shelves. The county lists droppings, gnawing, scratching sounds in walls, greasy stains and damaged food as rat signs.
If you find fresh droppings about half an inch long, it is rats. If they are the size of a grain of rice, it is mice. See rat droppings identification.
When the noise suddenly stops
If scratching that went on for weeks stops all at once, the rodents may have moved on, been trapped, or died inside a wall or the attic. Watch for a strong, sweet, rotten smell over the next few days. See dead rodent smell.
What to do next
Close and seal the attic hatch so nothing drops into the house. Trim branches back from the roof. Set snap traps where you find droppings. If the noises continue after a week of trapping, or you cannot reach the attic, have the house inspected. Ask for a written list of entry points. See rodent inspection.
Keep a short noise log
A simple log makes the pattern clear and helps anyone you hire. For three or four nights, write down the time you hear the sound, the room and roughly where in the ceiling or wall, what it sounds like and how long it lasts. Note anything else that changed, like a hot day, the AC running or a neighbor trimming trees. Patterns jump out fast. Sounds that start right after dark near one outside wall, then move across the ceiling, point to an entry at that wall. Sounds that only happen when the AC cycles point to the ducts, not rodents.