Ticking or Creaking Pipes When Hot Water Runs? Thermal Expansion, Not a Leak

Published by Clément Lacaille, Tech-Bharat · Updated September 13, 2026 · How we research

It's not a bang, and it doesn't happen the instant you turn a faucet off. It's a slower, quieter sound — a tick, a pop, or a soft creak that starts a few seconds after hot water begins running somewhere in the house, sometimes continuing on and off for a couple of minutes after you've shut the tap. It seems to come from inside a wall, from the attic, or from under the floor rather than from any one fixture, and it's easy to assume the worst: a leak, a structural problem, something expensive. Almost always, it's none of those things. It's the supply pipe itself getting longer as it heats up, and shorter again as it cools — and rubbing against wood framing or a loose metal strap every time it does.

Sorting it from every other pipe noise

California homeowners searching for a noisy-pipe fix usually land on one of four different problems, and the fix for one does nothing for the others:

• A single sharp bang the instant a valve, washing machine or toilet finishes shutting off is water hammer — a pressure-wave problem, covered in our banging pipes guide.
• A continuous tonal whistle or screech that lasts exactly as long as water is flowing, and stops the instant it stops, is a flow restriction — see our whistling and screeching pipes guide.
• Popping or rumbling from the water heater itself, with no tap open anywhere, is sediment baked onto the tank bottom — see our water heater noise guide.
• Hearing a shower or a toilet flush through a wall or ceiling from an adjacent room is sound transmission through the building structure, not a pipe problem at all — see our noisy pipes between floors guide.
• A slow tick, pop or creak that starts after hot water begins flowing and can continue for a minute or two after it stops, seemingly coming from a wall, attic or subfloor rather than a fixture — that's this article.

The physics: why a hot pipe gets longer

Every plumbing material expands when heated and contracts as it cools, proportional to both the temperature swing and the pipe's length. Copper's coefficient of linear thermal expansion runs around 1.7 × 10^-5 per °C; PEX runs roughly six to seven times higher, around 1.1-1.2 × 10^-4 per °C. In practical terms, a roughly 20-foot copper run carrying 140°F water through a 60°F attic can lengthen on the order of a fifth of an inch, and a 100-foot run can move close to a full inch across a 50°F-to-140°F swing. PEX moves considerably farther per foot for the same swing — which sounds like it should be noisier, but usually isn't, because it's soft enough to bend gently between supports instead of dragging against them, while stiffer copper transmits that movement as a distinct nudge. A 2025 materials-science study of cross-linked polyethylene pipe in ACS Omega by de Sousa and colleagues examined this thermo-mechanical behavior, tying PEX's response to temperature back to its cross-linked internal structure (see the study) — the material-level reason the same temperature swing sounds so different depending on what your pipes are made of.

The clicking itself has its own well-studied mechanism: stick-slip friction. A pipe creeping millimeter by millimeter against a wood joist or an undersized metal strap alternately grips and releases — grip while static friction holds, a tiny sudden slip once thermal force overcomes it, grip again a moment later. A 2025 multiscale review in Nonlinear Dynamics by Olejnik and Desta lays out stick-slip as a general source of intermittent, audible acoustic emissions wherever one surface creeps slowly against another under friction (see the study) — precisely what's happening at every point your supply line touches framing.

Why it shows up more in California homes right now

Three things push this from an occasional tick to a daily annoyance. An attic pipe run in the Central Valley or Inland Empire can swing 60-plus degrees on its own between a summer afternoon and a winter morning, before any water even runs, adding a full extra thermal cycle on top of normal use. A hot water recirculating pump keeps a loop of pipe near hot-water temperature for hours at a stretch instead of just during use, multiplying the number of heating-and-cooling cycles that same run of pipe sees each day. And on tankless units, the brief outlet-temperature dip owners know as the cold water sandwich is a real, repeated fluctuation right at the unit's own piping. None of these is dangerous on its own; they just add up to more ticking, in more houses, than older single-tank systems without recirculation used to produce.

Where to look, and what code already assumes

California's plumbing code already assumes this movement. Horizontal copper water piping 1 1/4 inch and smaller must be supported at least every 6 feet; horizontal PEX tubing 1 inch and smaller at least every 32 inches (48 inches for 1 1/4 inch and larger), and PEX clamps specifically must not restrict the tubing's ability to move as it expands and contracts. The code accounts for the pipe moving; it just doesn't guarantee that movement stays silent. A support installed to code can still tick if it's a rigid strap with no cushioning, or if the pipe was fished through a framing hole cut with zero clearance.

To find the contact point, the sound usually repeats from the same one or two spots rather than randomly, so listen along the accessible run — under a sink, in a closet with exposed plumbing, at the attic access — while someone runs hot water elsewhere. A bare metal strap, a pipe threaded through a tight joist hole, or a spot where a pipe rests directly on a stud are the usual culprits.

What fixing it costs

This is a low-stakes repair compared to almost anything else in a plumbing system, and most of the cost is access, not material:

• Cushioning an accessible contact point — wrapping foam pipe insulation around the pipe where it passes through a strap or joist, or swapping a bare metal strap for a cushioned/isolating clamp — typically runs $150–$400 for a service call covering one or two spots.
• Re-strapping or adding proper clearance at multiple points along an accessible run (a crawl space, garage ceiling, or open attic) commonly runs $300–$700.
• Opening a finished wall or ceiling to reach a contact point with no other access, patch included, typically runs $500–$1,500 depending on how much drywall repair follows.
• Adding an expansion loop or offset to a long, straight rigid-pipe run that's moving more than its supports were designed for is a less common fix, usually bundled into a repipe or remodel scope rather than billed as a standalone repair.

If the ticking traces to a recirculation loop or a tankless unit's cycling rather than a single bad strap, a plumber may instead recommend adjusting the recirculation schedule or aquastat setting, which costs nothing beyond the visit itself.

When it's more than an annoyance

Ticking on its own is cosmetic, but two situations deserve more attention. If it's been going on for years unaddressed, sustained rubbing at one point can eventually wear through pipe insulation or even thin-wall tubing — the same abrasion mechanism behind hot-side slab leaks, where a pipe repeatedly expanding against concrete or rebar wears through over time; see our guide on slab leak signs, causes and repair if the sound is coming from a slab-on-grade line rather than a wall or attic. And if the noise is new and loud, starting right after a repipe, remodel, or new tankless or recirculation install, it's worth a call back to whoever did that work — inadequate clearance at the framing is an easy, fixable oversight, not something to live with in a brand-new system. Our copper vs. PEX repiping guide compares the two materials more broadly if a persistent noise problem has you weighing a larger repipe.

If a ticking or creaking pipe in your house has you wondering whether it's something more, or you'd rather have a professional confirm and fix it in one visit in Fresno, Riverside or San Jose, request a free quote on Plumber Comparator and get matched with a licensed local plumber.

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