Knocking Noise in Walls at Night and How to Find the Cause

It starts at around 11pm, just after the heating clicks off: a sharp knock somewhere behind the bedroom wall, then two more, then silence. By the third night you are lying awake counting them. Most people who hear a knocking noise in walls at night assume the worst: rats, a failing boiler or something they would rather not name. In my experience the cause is usually ordinary, and you can narrow it down in an evening with nothing more than a notebook and a bit of patience.

The trick is to treat it like a small investigation. When does it happen, where is it loudest, and what changed in the house just before it starts? Those three questions eliminate most suspects before you open a single cupboard. Here is the method I use, and the culprits it usually turns up.

Start a Noise Log Before You Guess

Write down every knock for three or four nights. Record the time, the room, how many knocks, and what was happening in the house at that moment: heating switching on or off, someone running a tap, the dishwasher finishing, a cold night after a warm day.

This sounds tedious, but it is the single most useful step. In one flat I helped with, the log showed the knocks began within two minutes of the upstairs neighbour's shower every evening at 10:40. Without the times written down, nobody had connected the two.

Next, pin down the location. Sound travels along pipes and joists, so the room where you hear it is not always the room where it starts. Press your ear, or the open end of an empty glass, against the wall at a few points and move towards the loudest spot. A phone voice recorder left running in different rooms on separate nights works too. Compare the volume of the recordings and you will usually find one wall, or one stretch of floor, that is clearly louder than the rest. That is where you start looking.

Match the Timing to the Usual Suspects

Once you have a few nights of notes, the timing usually points to one of a handful of causes:

When it happens	Likely cause	What it sounds like
Heating starts or stops	Pipes expanding or contracting	Ticking or sharp knocks, slowing down
A tap or valve closes quickly	Water hammer	One loud bang, sometimes a shudder
Late evening, cool nights	Timber framing cooling	Random single cracks or pops
Windy weather	Loose cladding, vent flaps, cables	Irregular tapping or rattling
Dusk and dawn, any weather	Rodents or birds	Scratching, scurrying, light taps

Most homes have more than one source. Fix the loudest pattern first and see what is left.

Heating Pipes That Tick and Knock

Copper and plastic pipes grow slightly longer when hot water flows through them. If a pipe is clipped too tightly, or rubs against a joist where it passes through, it sticks and then jumps, producing a knock. The noise typically comes in a series for 10 to 20 minutes after the heating switches on or off, then stops.

The fix is usually simple once you find the spot: loosen an overtight clip, add a rubber-lined clip, or slip a bit of foam insulation around the pipe where it touches wood. Under-floor runs are the usual offenders, so start by lifting a board near the radiator closest to the noise.

Water Hammer When a Tap Closes

Water hammer is the loud single bang you hear when a tap, washing machine valve or toilet cistern valve shuts suddenly. Moving water has momentum, and when it stops abruptly the pressure spike shakes the pipe. It often sounds like it comes from a different room, because the pipe carries the shock.

Check whether the bang lines up with appliances finishing a fill cycle. Fitting a small water hammer arrestor near the offending valve, or lowering very high mains pressure with a pressure-reducing valve, usually cures it. Very high pressure also wastes water, so if your bills have been creeping up, our guide to tracking down a hidden water leak at home is worth a read at the same time.

Why You Should Not Jump Straight to Pest Control

The common advice online is that any noise inside a wall at night means mice or rats, and that you should call pest control straight away. I think that is backwards. A pest visit can cost a fair amount for an inspection, and many technicians will lay bait whatever they find.

Rodents leave evidence. Before calling anyone, look for droppings along skirting boards and in cupboards under sinks, chewed food packaging, greasy smear marks at gaps, and a musty smell. Animals also make soft scratching and scurrying noises, not sharp regular knocks. If your log shows knocks tied tightly to the heating schedule and there is no other evidence, the pipes are far more likely than pests. If you do find droppings, then a professional is the right call.

Timber, Weather and Settling

Wooden floors, roof timbers and stud walls shrink slightly as the house cools at night. This produces random single cracks, often loudest in the first cold weeks of autumn and in newer homes during their first few years. It is normal and rarely signals structural trouble. A thermostat set a degree or two higher overnight often softens it, because the timber cools more slowly and releases its stress in smaller steps.

Windy nights add another set of noises: a loose vent flap, a satellite cable tapping on render, a gutter bracket working loose. Walk round the outside of the house on a breezy evening and listen at the wall where the noise is loudest inside.

When to call a professional

New cracks in plaster appearing alongside the noises
Doors or windows that suddenly stick
Knocking from the boiler itself, which can indicate scale or a pump problem
Any burning smell or electrical buzzing near sockets

FAQ

Why does the knocking only happen at night?

Night is when heating schedules switch off, temperatures drop and the house is quiet enough to hear small sounds. Noises that happen all day often only become noticeable in bed.

Can knocking pipes cause damage?

Expansion ticks are mostly harmless, but repeated water hammer can loosen joints and fittings over time. It is worth fixing within a few weeks rather than ignoring it.

How can I tell if it is an animal?

Animals make scratching, scurrying or chewing sounds that move around, usually at dusk and dawn. Look for droppings and gnaw marks. Regular knocks at fixed times point to plumbing instead.

The Practical Takeaway

Keep a noise log for three nights, write down exactly when each knock happens, and compare it with your heating timer and water use. Nine times out of ten, the pattern points straight to a pipe or valve you can fix cheaply. For more household mysteries solved step by step, browse our living section.