Scratching in Your Walls at Night? What That Sound Means in an Ontario Home

Quick answer: Scratching inside a wall after dark in late August almost always means mice. Light, fast, scratchy sounds low in a wall between 9 p.m. and 2 a.m. are mice; heavier scampering or rolling sounds in the morning are usually squirrels; slow, heavy thumping overhead is a raccoon; and soft fluttering at dusk points to bats. The sound matters less than what it proves — something found a way in, and that entry point will keep working all winter. Do not seal the wall while an animal is inside it. Call Sani IQ at (705) 302-1887 for a $95 inspection, credited when you book the treatment.

Why the noise starts in late August

You lie down, the house goes quiet, and there it is — a light scratching somewhere in the wall behind the headboard. It stops when you knock. Twenty minutes later it starts again.

Almost every Ontario homeowner who calls us about this calls in the same six-week window: late August through early October. That is not a coincidence.

Ontario nights start dropping into single digits in the last week of August. House mice have no fat reserves to speak of and no ability to hibernate, so a cold night is an immediate survival problem for them. Meanwhile the outdoor food supply is peaking and their summer breeding season has produced the largest population of the year. You have maximum mouse numbers arriving at exactly the moment they need shelter — and your exterior wall is the warmest, driest, safest structure within a hundred metres.

They do not chew a hole to get in. They find one that already exists. A mouse fits through a gap the width of a pencil, and the average Ontario home has a dozen of them: the gap where the dryer vent penetrates the siding, the gap under a garage door corner, the utility line entry behind the meter, weep vents in brick, a lifted soffit corner, the space where the deck ledger meets the wall.

Decoding the sound: what’s actually in there

The species matters, because the treatment is completely different. Here is the matrix we use on the phone.

Mice — Light, fast, scratchy or scurrying. Often a faint gnawing. Usually low in the wall or between floors, and it moves along the wall rather than staying in one spot. Peak activity 9 p.m. to 2 a.m., and again briefly before dawn. If you knock, it stops for a few minutes and resumes. This is the most common answer by a wide margin in late August.

Rats — Same nocturnal window but heavier and slower, with more audible gnawing. More common in older Toronto-area housing stock, near construction, and close to commercial food waste. If you’re hearing this in a basement wall or under a floor rather than up high, take it seriously.

Squirrels — Heavier scampering, and the giveaway is timing: squirrels are diurnal. If the noise is loudest at sunrise and again in late afternoon and the house is quiet at midnight, it isn’t mice. You may also hear rolling — that’s a nut or acorn being moved. Usually in the attic or upper wall, not the basement.

Raccoons — Slow, heavy thumping and dragging. You will hear weight. Usually overhead in the attic rather than inside a wall cavity, most active shortly after dusk. In spring you’d also hear chittering from kits; in late summer it’s usually a single adult. Damage is on a different scale entirely.

Bats — Soft fluttering, scratching or a faint squeaking, concentrated right at dusk and again at dawn as they leave and return. Usually in an attic, soffit, or the space behind fascia. Bats are protected in Ontario and cannot be trapped or killed — exclusion is legally required and timing-sensitive.

Birds — Rustling and chirping during daylight only, usually near a bathroom or dryer vent where a nest has been built in the ducting.

If you’re unsure which one you have, our mice and rodent library page covers droppings, gnaw marks and runway signs that let you confirm the ID visually rather than by ear.

The thing homeowners get wrong: sealing the wall

The instinct is to find the hole and plug it. If you do that while the animal is inside the wall, you have made the problem worse in three ways.

The animal doesn’t leave — it dies in the cavity, and you now have an odour problem lasting two weeks to two months somewhere you can’t reach without opening drywall. Second, a trapped mouse chews laterally to escape, which is how wiring damage happens. Third, you’ve lost the ability to trap it on its own runway, which was the fastest route to resolving it.

The correct order is always: confirm the species, remove the animals, then seal the entry points. Reversing those steps is the single most expensive DIY mistake we get called to fix.

Why walls mean an entry point, not a one-off

Here is the part that matters more than the noise. A mouse in a wall cavity is not a mouse that wandered in through an open door. Wall voids connect to the exterior — that’s the whole point of the structure. If something is living in there, it has a route in from outside, and that route works every night.

It also means you almost certainly do not have one mouse. Mice follow scent trails, and the pheromone marks along a runway advertise the route to every mouse within range. A single female produces five to ten litters a year, with young breeding at about six weeks. A pair in late August is a serious infestation by Christmas.

The damage is measurable: shredded insulation loses R-value, gnawed wiring is a fire risk most homeowners never see, and droppings contaminate insulation that eventually needs replacing. The cost of ignoring a scratching sound in September is usually paid in January, at a higher number.

We see this pattern across York Region every fall — the older subdivisions in Richmond Hill and the ravine-backing properties in Oakville generate the most late-August calls, because mature landscaping and established rodent populations sit right against the building envelope.

What to do this week

Find where the sound is loudest. Note the wall, the height, and the exact times you hear it. This narrows the inspection enormously and it’s genuinely useful information to give a technician.

Check the obvious signs. Droppings behind the stove, under the sink, along baseboards, and in the back of pantry shelves. Grease smudges along a baseboard where fur repeatedly rubs the same path. Shredded paper or insulation in a corner. Gnaw marks on food packaging.

Do a perimeter walk in daylight. Check every point where something penetrates the exterior wall — dryer vent, AC line set, gas meter, hose bib, cable entry — plus the bottom corners of the garage door. You’re looking for gaps you could push a pencil into.

Don’t start with hardware-store bait. Bait placed away from actual runways does nothing, and bait used indoors without knowing where the animal travels produces exactly the die-in-the-wall outcome described above. Snap traps on confirmed runways work far better — but you have to know where the runways are.

Do not seal anything yet. See above.

What professional treatment actually involves

An inspection is the part that matters. Our technicians identify the species from physical evidence rather than guessing from a description, map the runways inside the structure, and find the actual entry points on the exterior — which are almost never where homeowners expect. Then treatment is placed on the runways, and exclusion work seals the building envelope once the interior is clear.

Our One-Time Mice Treatment is $345, and Complete Mice Protection is $495. Every service starts with a $95 professional inspection, credited in full when you book the treatment, and one-time services carry a 60-day guarantee.

But be honest about what a one-time service does. It resolves the mice that are in your wall right now. It does not change the fact that your house sits in a neighbourhood with a permanent rodent population, and that every autumn that population comes looking for shelter again. Homeowners who treat reactively tend to call us every single fall.

Complete Mice Protection at $895 per year is the plan we actually recommend to anyone who has heard scratching in a wall, because rodent pressure is annual and recurring by nature. It covers scheduled monitoring and treatment through the seasons rather than one incident, so the fall wave is intercepted before it’s audible from your bedroom. If you also want insects covered, Essentials at $1,195 bundles both.

The way to think about it: the one-time treatment ends tonight’s problem, and the annual plan is what stops you paying for it again next September and the one after. Take our free quote quiz for a price on your address in about a minute, or see the full range of residential pest control services we run across the GTA, York and Durham Regions, Simcoe County, Barrie, Orillia and Muskoka.

Sani IQ is BBB Accredited with a 5.0 rating across 126 Google reviews, carries $5M liability, and is licensed under the Ontario Pesticides Act and registered with the MECP. Our technicians are employed, licensed and background-checked — never subcontracted.

Frequently asked questions

Is scratching in the wall always mice? No, but in late August in Ontario it usually is. The reliable tell is timing: mice and rats are active 9 p.m. to 2 a.m.; squirrels are loudest at sunrise and late afternoon; raccoons thump heavily just after dusk; bats flutter at dusk and dawn.

Can I just wait for it to go away? It won’t. An animal that has found a warm wall cavity in late August has found its winter quarters, and mice breed year-round indoors. What you hear in September is smaller than what you’ll hear in December.

Why does the scratching stop when I bang on the wall? Because they freeze when startled and resume once the threat passes — usually within a few minutes. It confirms something living is in there, but it doesn’t tell you the species.

Is a mouse in the wall a fire risk? Gnawed wiring is a recognized risk with any rodent in a structure. Mice gnaw constantly to manage incisor growth, and wiring inside a wall cavity is a common target. It’s one of the main reasons we treat wall-void activity as urgent rather than cosmetic.

Should I put poison in the wall? No. Bait placed in an inaccessible void produces an animal that dies where you can’t reach it, and the resulting odour lasts weeks. Interior work should be trap-based and placed on identified runways.

How long does it take to resolve? Most residential mouse jobs are resolved over two to three visits across a few weeks — initial treatment, a follow-up to confirm the interior is clear, then exclusion work on the entry points. Call (705) 302-1887 and we’ll tell you what your specific situation likely needs.