Mice in the Walls: Signs, Causes and How to Get Them Out

Mice or something else?

Wall noises have several possible causes. Mice make light, quick scratching and scurrying, often in short bursts, sometimes with faint squeaks. Roof rats are heavier: thumps, louder gnawing and running along the top of a wall or across the ceiling. Pipes ticking as they cool, or wood creaking as the house cools at night, can fool you too, but those sounds are regular and do not move around.

If you find droppings the size of a grain of rice under the sink, behind the stove or in a closet on the same wall, mice are the likely answer. See rodent noises at night and mouse droppings identification.

How mice get into walls in San Diego homes

Most San Diego houses are stucco over wood framing. The wall cavities are closed at the sides but often open where something passes through the top or bottom plate. Common routes:

• From the attic, through gaps where wires, plumbing vents or ducts pass down into the wall
• From the crawl space in older raised-floor homes in neighborhoods like North Park, Kensington and Ocean Beach
• From the garage, through gaps around the water heater, laundry hookups or the panel
• From outside, through gaps at the weep screed at the base of stucco walls, or around AC line sets and cable lines
• From inside, through gaps behind the stove, dishwasher, fridge and under sinks, where walls are often left open around pipes

Kitchen remodels and new HVAC or solar work often leave new holes in the plates.

Find the entry and exit points

Mice come out of the wall to eat and drink. Look for:

• Droppings clustered at one spot under a sink or behind an appliance
• Gaps around pipes where they enter the wall
• Gnawed edges on baseboards or the back of lower cabinets
• Grease smudges at the edge of a gap
• Droppings in the attic right above the wall where you hear sounds

Those are the points to trap and later seal. Note the time of night and whether the sounds move up and down, which points to an attic route, or along the wall, which points to a route at floor level.

Trap at the openings

Set snap traps flat against the wall with the trigger end facing the gap, right where the mice come out. Use small amounts of peanut butter as bait. Put traps under the sink, behind the stove and in the attic above the wall. Check them daily and handle catches with gloves and disinfectant.

Avoid poison bait in the house. A poisoned mouse often goes back into the wall to die, and that smell can last for weeks. California law also bars most residential use of anticoagulant baits: AB 1788 has covered the second-generation products since 2021, and AB 2552 added chlorophacinone and warfarin on January 1, 2025. See dead rodent smell.

Seal the route

Once catches stop, seal the openings. Inside, pack copper or steel mesh around pipes and finish with sealant. Outside, close gaps at the weep screed and around lines with mesh and an exterior sealant. In the attic, seal around wires and pipes where they drop into the walls. The county's hantavirus brochure says to seal holes dime-sized or larger and recommends 1/4 inch wire mesh for repairs.

If you seal while mice are still inside the wall, they will chew out somewhere else or die inside. Trap first, then seal.

When to call for help

Call if the sounds continue after a week of trapping, if you cannot find the entry points, if you smell something dead, or if you hear rats rather than mice. A technician can check the attic and crawl space, find the route and seal it. See mice in walls removal.

What it says about the rest of the house

Mice in one wall usually mean a route that serves more than one room. If the sound is in a kitchen wall, check the bathroom or laundry that shares the same plumbing chase. If it is in a bedroom wall on the garage side, check the garage for droppings and gaps. Also look at the outside of that wall for gaps at the base of the stucco and around utility lines. Fixing the whole route is what keeps the noise from moving to the next wall a week later.