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Banging, Knocking, and Humming Pipes: What Causes Them
Water hammer, loose pipe clips, and expanding hot pipes each make a different sound — and need a different fix.
Marcus Ibe · Oct 25, 2026 · 6 min read · 5 steps
Noisy pipes are rarely dangerous, but they are annoying, and some noises are warning signs of pressure problems that can strain joints and appliances over time.
Listening carefully to when the noise happens is the fastest way to find the cause.
A loud bang when a tap closes
This is water hammer: a shock wave created when fast-moving water stops suddenly, often when a washing machine or dishwasher valve snaps shut. It can loosen joints over time. Fitting a water-hammer arrestor near the appliance, reducing high mains pressure with a pressure-reducing valve, or securing loose pipe runs usually solves it.
Ticking or creaking as heating warms up
Copper pipes expand as they heat and contract as they cool. Where they pass through tight holes in joists or rub against clips, they creak or tick. Adding felt or foam padding at contact points, or slightly enlarging notches in joists, allows the pipes to move quietly.
Rattling when water runs
Pipes that are not clipped firmly can vibrate against walls and floors. Check accessible pipe runs under floors, in cupboards, and in lofts, and add clips every metre or so on horizontal runs.
Humming or whistling
- A whistle from a single tap often means a worn washer or partly closed valve
- A hum throughout the house can point to very high water pressure
- Gurgling from radiators suggests trapped air — see our radiator bleeding guide
- Kettling (rumbling) from a boiler can indicate limescale build-up
When to call a plumber
If noises start suddenly, get worse, or come with leaks, damp patches, or pressure changes, ask a plumber to check. Boiler noises should be looked at by a qualified heating engineer.
This is general home-maintenance information, not professional advice. Building codes, permits, and safe practices vary by location — consult a licensed contractor, electrician, or plumber for work beyond your experience.