Water Heater Making Noise: Popping, Rumbling, and Whistling Explained

Your water heater works quietly in the background most of the time, so when it starts making strange noises, it’s hard to ignore. Popping, rumbling, whistling, and banging sounds aren’t just annoying — they can be early warning signs of underlying problems that, left unaddressed, could lead to costly repairs or even a complete system failure. Understanding what these sounds mean is the first step toward protecting your investment and keeping hot water flowing reliably in your home.

Whether you have a traditional tank-style heater or a modern tankless unit, knowing how to interpret the sounds your system makes can save you time, money, and a lot of cold showers. The experts at Doctor Water Heater have seen it all, and in this guide, we’ll walk you through the most common water heater noises, what causes them, and what you should do about each one.

Popping or Crackling Sounds

Of all the noises a water heater can make, popping or crackling is probably the most common complaint homeowners report. This sound is often described as similar to a coffee percolator or a pot of water coming to a boil — which is actually not far from what’s happening inside your tank.

What Causes It

The primary culprit behind popping sounds is sediment buildup at the bottom of the tank. Over time, minerals naturally present in your water supply — primarily calcium and magnesium — settle out and accumulate on the tank floor. When your heating element or burner fires up, water trapped beneath this layer of sediment heats rapidly and forces its way through, creating those characteristic popping and crackling sounds.

Hard water areas are especially prone to this problem. If your home has hard water, mineral deposits can build up surprisingly quickly, sometimes within just a year or two of a new installation.

Why It Matters

Beyond the noise, sediment buildup is genuinely harmful to your water heater. It acts as an insulating barrier between the heat source and the water, forcing the system to work harder and longer to reach the target temperature. This drives up your energy bills and puts extra stress on the tank lining and heating elements, shortening the overall lifespan of the unit.

What to Do

Flushing your water heater tank at least once a year is the best way to combat sediment buildup. This involves attaching a hose to the drain valve and allowing the water (and sediment) to flow out until it runs clear. If the buildup is severe and flushing doesn’t resolve the noise, it may be time to call a professional. In some cases, the tank lining may already be compromised, making replacement the more cost-effective option.

Rumbling Sounds

Rumbling is closely related to popping but tends to indicate a more advanced stage of sediment accumulation. Where popping is sharp and intermittent, rumbling is often a low, continuous sound that occurs during the heating cycle.

What Causes It

When sediment has accumulated to a significant degree, the entire heating process becomes turbulent. Water moving through and around a thick layer of mineral deposits produces a rumbling or rolling sound, similar to distant thunder. In gas water heaters, this can also be accompanied by changes in the flame behavior as the burner struggles to heat through the sediment layer efficiently.

Why It Matters

A rumbling water heater is typically one that has been overdue for maintenance for some time. The heater is working significantly harder than it should, consuming more energy with each heating cycle. In gas models, inefficient combustion caused by sediment can also be a safety concern, as it may affect the venting of combustion gases.

What to Do

Start with a thorough tank flush. If the rumbling persists after flushing, the sediment may have hardened and bonded to the tank interior, making it impossible to remove through flushing alone. At this stage, a professional assessment is strongly recommended. Depending on the age and condition of the unit, replacement may be more economical than continued repair.

Whistling or Screeching Sounds

Unlike popping and rumbling — which are typically sediment-related — whistling and screeching sounds usually point to issues with water flow or pressure. These noises tend to be higher-pitched and may occur even when the heater isn’t actively heating.

What Causes It

The most common source of whistling is a partially closed or faulty valve. The temperature and pressure relief (T&P) valve, inlet valve, or outlet valve can all produce a whistling noise when water is being forced through a narrow or obstructed opening. Think of it like blowing air through a small gap — the restriction creates the sound.

A failing T&P valve is a particularly important one to watch for. This valve is a critical safety device designed to release pressure if the tank reaches dangerous levels. When it begins to wear out, it may start venting steam or water in small amounts, producing a hissing or whistling noise in the process.

Additionally, high water pressure in your home’s plumbing system can cause whistling as water enters the tank. Most residential systems operate safely between 40 and 80 PSI, and anything above that range can stress your plumbing and appliances alike.

Why It Matters

Whistling related to the T&P valve should never be ignored. This valve exists specifically to prevent tank rupture in the event of excessive pressure or temperature. A valve that is leaking or malfunctioning is not providing the level of protection it should. Ignoring this warning sign can have serious consequences, including tank failure.

High water pressure is similarly a whole-home concern. It doesn’t just affect your water heater — it puts stress on every pipe, fitting, and appliance in your home.

What to Do

Check all valves connected to the water heater to make sure they are fully open. If the noise appears to be coming from the T&P valve, do not attempt to test or manipulate it yourself unless you know exactly what you’re doing — contact a licensed plumber or water heater specialist. If high water pressure is suspected, a pressure gauge can be attached to an outdoor spigot to check the reading. A pressure-reducing valve (PRV) installed on the main water line can bring pressure into the safe range.

Banging or Knocking Sounds

Banging and knocking — sometimes called “water hammer” — is a jarring sound that occurs suddenly, often right after a tap is shut off or the water heater finishes a heating cycle.

What Causes It

Water hammer is caused by the sudden stopping of water flow in your pipes. When a valve closes quickly, the momentum of the moving water has nowhere to go, sending a shockwave through the plumbing that produces a loud bang or series of knocks. It can also occur inside the water heater tank itself if thermal expansion is pushing against the tank walls or connected pipes.

In homes without expansion tanks, the pressure created as water heats and expands has to go somewhere. If the system is a closed loop (common in homes with backflow preventers or pressure-reducing valves), that expanding water can cause banging and stress on the tank.

Why It Matters

Water hammer isn’t just noisy — over time, the repeated shockwaves can loosen pipe joints, damage valves, and stress solder connections throughout your plumbing. Thermal expansion issues can shorten the life of your water heater and increase the risk of leaks.

What to Do

Water hammer can often be resolved by installing water hammer arrestors — small devices that absorb the shockwave when water flow stops suddenly. These are relatively inexpensive and can be installed at key points in your plumbing without a major renovation. For thermal expansion issues, installing an expansion tank alongside your water heater gives expanding water a safe place to go, relieving pressure from the main tank.

Hissing Sounds

A hissing sound coming from your water heater is one that warrants prompt attention. Unlike the other noises discussed here, hissing often indicates an active leak rather than a developing maintenance issue.

What Causes It

When water contacts a hot surface — such as the burner or flue in a gas water heater — it instantly vaporizes into steam and produces a hissing sound. This typically means water is leaking from somewhere inside the unit and dripping onto a hot component. The leak may be coming from a faulty connection, a cracked tank, or a failing element gasket in an electric model.

Hissing can also occur when the T&P valve is actively releasing steam due to excessive pressure — again pointing back to the importance of that safety device.

Why It Matters

A leak inside a water heater is a serious issue. Water damage, mold growth, and the risk of electrical hazard (in electric models) or gas-related issues (in gas models) make this a situation that calls for immediate action.

What to Do

If you suspect an active leak, turn off the power or gas supply to the unit and shut off the cold water inlet valve. Inspect the area around the heater for visible water. Contact a professional as soon as possible — hissing accompanied by a water leak is not a DIY fix for most homeowners.

Ticking or Tapping Sounds

Ticking and tapping noises are among the less alarming sounds a water heater can make, but they’re worth understanding so you know when they’re normal and when they’re not.

What Causes It

Most ticking and tapping sounds in a water heater are caused by normal thermal expansion and contraction of the pipes connected to the unit. As metal pipes heat up and cool down, they expand and contract, and this movement can cause them to tick or tap against pipe straps, wall studs, or other surfaces.

Some water heaters also have heat traps — small devices built into the inlet and outlet nipples that prevent convection currents from moving heated water back into the cold supply line. These heat traps contain small balls or flappers that can produce a ticking sound as water moves past them.

Why It Matters

In most cases, ticking and tapping are harmless. However, if the sound is loud, persistent, or accompanied by other symptoms, it’s worth investigating further to rule out a more serious cause.

What to Do

Inspect the pipe connections and ensure they are properly secured and insulated where they contact hard surfaces. If the sound is coming from heat traps and becomes bothersome, a plumber can replace them with a straight-nipple version — though this does reduce the energy efficiency of the unit slightly.

When to Call a Professional

Some water heater noises are manageable with basic DIY maintenance — flushing the tank, checking valves, and ensuring pipes are properly secured. But others are clear signals that professional help is needed. You should contact a licensed technician when:

• Noises persist after flushing the tank and checking all valves
• You notice visible leaks, water damage, or moisture around the unit
• The T&P valve appears to be releasing steam or water
• You smell gas near a gas water heater
• The unit is more than 10–12 years old and showing multiple symptoms
• Hot water output has decreased significantly alongside the noise

The team at Doctor Water Heater specializes in diagnosing and resolving exactly these kinds of issues. Rather than guessing at the cause of a noise or risking further damage with an uninformed fix, having a professional evaluate the system ensures the problem is correctly identified and addressed the first time.

Preventive Maintenance: The Best Defense

The good news is that most water heater noise problems are preventable with consistent maintenance. A few simple habits can keep your system running quietly and efficiently for years longer than a neglected unit:

Annual flushing removes sediment before it has a chance to harden and bond to the tank. This is the single most impactful maintenance task for tank-style water heaters.

Anode rod inspection should be done every two to three years. The anode rod is a sacrificial metal rod inside the tank that corrodes in place of the tank lining. When it’s depleted, the tank itself becomes vulnerable to corrosion. Replacing it proactively extends tank life significantly.

Temperature setting check ensures the thermostat is set to 120°F, which is the recommended temperature for safety and efficiency. Settings that are too high increase pressure, energy consumption, and the risk of scalding.

Pressure checks help you stay ahead of high water pressure issues before they cause damage to your plumbing system or appliances.

Professional inspections every few years give a trained eye the chance to catch problems — like early corrosion, sediment that can’t be flushed, or a failing T&P valve — before they escalate into emergencies.

Final Thoughts

A noisy water heater is your system’s way of asking for attention. Whether it’s popping from sediment, whistling from a faulty valve, rumbling from years of neglect, or banging from water hammer, each sound tells a specific story about what’s happening inside the unit. Listening to those signals — and acting on them promptly — is what separates a well-maintained water heater that lasts 15 years or more from one that fails prematurely.

Don’t wait until you’re standing under a cold shower to investigate strange sounds. The earlier you address a noise concern, the more options you’ll have — and the less it’s likely to cost. For expert guidance, diagnosis, and repair, Doctor Water Heater is ready to help you get to the bottom of any water heater noise problem quickly and effectively.