Scratching Noises in Your Walls or Attic at Night? Here's What It Usually Is

In the San Gabriel Valley, scratching in the walls or attic after dark is usually one animal: the roof rat. They're nocturnal, they're superb climbers, and our mature trees, citrus, ivy and utility lines give them a highway straight onto the roofline. But the timing and character of the noise narrows it down fast — here's the field guide I run through on every one of these calls.

What the timing tells you

The rule of thumb: night noise points to rats and mice, day noise points to squirrels and birds. Rats also tend to run the same routes at the same times — people tell me they can nearly set a clock by it.

Confirming it's rats without going up there

• Droppings — roof rat droppings are about half an inch long, spindle-shaped with pointed ends. You'll find them along garage walls, in the attic, or near pet food.
• Gnaw marks — fresh, pale tooth marks on wood, plastic bins, wiring insulation or irrigation lines. Rats gnaw constantly because their teeth never stop growing.
• Rub marks — greasy smudges along beams and entry holes from their fur.
• The neighborhood check — fruit trees with hollowed-out fruit, ivy-covered fences and pool equipment areas are classic roof rat territory. I wrote more about that in roof rats and citrus trees.

Why tossing poison in the attic backfires

It's the most common DIY move and the one I most wish people would skip. A poisoned rat usually dies somewhere you can't reach — inside a wall void or under insulation — and the odor that follows is memorable. California has also restricted many of the strongest rodenticides precisely because they move up the food chain to owls, hawks and pets. And poison does nothing about the actual problem: the openings the rats are using to get in.

What actually works

The fix that lasts is mechanical, not chemical: trap what's inside, seal every way in, and clean up what they left behind. Rats can squeeze through a gap the size of a quarter — attic vents with torn screens, gaps where cables enter, unscreened roof returns and lifted tile edges are the usual doors. Sealing those (exclusion) is the difference between solving the problem and renting it back every winter. One caution before you touch anything up there: rodent droppings shouldn't be swept or vacuumed dry — read why, and what to do instead.

If the noise is nightly, it isn't going away on its own — colonies grow toward food, not away from it. A proper rodent inspection finds the entry points, and a trap-and-seal program with real follow-up ends it.