Fix it
Why are my pipes making a knocking noise?
Pipe knocks divide cleanly by trigger: a bang when a valve closes is water hammer, ticking as hot water flows is expansion, and rattling during use is a loose pipe drumming on the framing it should be strapped to.
What it usually is
-
Water hammer at fast-closing valves
Washing machines and dishwashers snap their valves shut against moving water; the momentum bangs the line like a struck bell. One sharp bang tied to an appliance cycle is the signature.
-
Thermal expansion ticking through framing
Hot water lengthens copper enough to creak through joist holes and against straps — a fading tick-tick after hot water runs, most audible at night.
-
Loose strapping letting pipes rattle
A pipe with a failed strap knocks with every flow change, from any fixture, and you can sometimes silence it by hand pressure on the access-visible section.
-
High water pressure amplifying everything
Pressure above about 80 psi makes every close bang harder and every appliance work sooner. A $12 gauge on a hose bib answers this in one minute.
What you can check yourself
Identify the trigger fixture. Gauge the pressure at an outdoor spigot. For hammer, arrestors screw onto washer connections DIY-style. Accessible rattling pipes can be re-strapped or cushioned with pipe insulation where they cross framing.
When it’s a job for a pro
Pressure over 80 psi calls for a pressure-reducing valve at the main — plumber work that also protects every appliance you own. Hammer or rattling inside closed walls is judgment about where to open, which is exactly what experience is for.
Screw-on arrestors are $15 to $30 DIY; a pressure-reducing valve typically runs $250 to $600 installed; in-wall re-strapping depends on access, commonly $150 to $500.
Ready for a plumber? Get matched now
Enter your ZIP and we match you with an independent local partner for exactly this kind of job.