Why Your Water Heater Might Be Making Noise

Your hot water tank makes specific noises based on what's going wrong inside. Learning what each sound means helps you describe the issue accurately when you call for service:

Popping and Crackling Sounds

Popping starts when steam bubbles force their way through mineral deposits stuck at the bottom of your tank. The heating element makes steam under this sediment layer. When the bubbles break through, you get that pop, like a kernel bursting in a hot pan. Crackling goes along with popping. Both come from sediment buildup, and flushing the tank gets rid of them.

In some cases, crackling can also be caused by aluminum hydroxide, jelly-like beads that form when an aluminum anode rod reacts with chlorine in your water. If you see green, blue, or gray beads when flushing your tank, ask your plumber about switching to an aluminum-zinc anode rod.

Leaking hot water around your tank base and popping noises often happen together. The sediment causing those sounds speeds up the rust that creates leaks.



Rumbling and Gurgling Noises

Rumbling sounds like thunder rolling through your basement. This happens when sediment has piled up enough to block normal water flow inside the hot water tank—water trying to heat and rise has to push around mineral chunks, creating that rolling sound. Gurgling means air is trapped somewhere in your system, and you can hear it when turning on the hot water after the tank hasn't run for a while.

Humming or Buzzing

Humming sounds usually come from loose parts vibrating as your water heater runs. Screws work themselves loose over time, brackets shift, and components that should sit firmly start to rattle. Electric water heaters can also hum if the heating element vibrates against the tank wall. These sounds are typically harmless but can get annoying. Tightening loose screws and connections usually solves the problem.

If you have an ultra-low NOx water heater, humming may indicate a damaged burner rather than loose parts. Contact A. O. Smith support to diagnose the issue and determine if you need a repair.

High-Pitched Whistling or Screeching

A high-pitched screeching or whistling sound needs immediate attention. Whistling happens when water squeezes through a space that's too small such as a valve that's partly closed, a clogged pressure relief valve, or sediment blocking the normal flow. Mechanical screeching comes from worn-out parts. In gas water heaters, blower motor bearings wear down. In electric tanks, heating elements get damaged and start making noise.

Your water heater maintenance checklist should include listening for new sounds every few months. Noise starts quietly and gets louder as sediment builds up or parts wiggle loose.

Once you know what sound you're hearing, pinpointing the cause gets easier. Three problems create most water heater noises:

Sediment Buildup in the Tank

Minerals in your water supply like calcium and magnesium, settle at the bottom of your tank over time. Hard water speeds this up because it carries more minerals. Every time your hot water tank heats water, more minerals sink and join the growing layer of gunk at the bottom. This layer creates a barrier between your heating elements (in electric water heaters) or burner (in gas water heaters) and the water above it, making your water heater work harder to reach the right temperature.

It also traps steam bubbles underneath, which causes those popping sounds, and takes up space where hot water should be. When you ignore this problem, your tank wears out faster, and your energy bills climb.

Loose Heating Elements and Parts

Water heaters vibrate while they run. After years of heating cycles, screws loosen, brackets shift, and parts that should sit tight start to wiggle. These loose pieces vibrate against the tank or rattle against each other, creating humming, buzzing, or clanking sounds.

Heating elements can also work loose where they connect to the tank, vibrating as water flows past them. Hot and cold cycles make metal expand and contract, gradually loosening screws, even those installed correctly.

Water Pressure and Flow Issues

Water entering your tank under high pressure can cause banging, called water hammer. This happens when fast-moving water suddenly stops, like when a valve slams shut, and the momentum creates a shock wave that bangs through your pipes into the tank. High water pressure stresses your plumbing and makes normal water flow louder.

Blockages from partially closed valves or sediment buildup force water through tight spaces, creating whistling sounds. Heat trap nipples, fittings that prevent heat from escaping up your pipes, can also tick or click as hot water expands and contracts inside them during heating cycles.

Knowing what's causing the noise tells you what needs fixing. Here's how to address the problem and get your tank running quietly again:

When to Call a Professional Plumber

Some water heater noise requires a trained technician with advanced tools and experience. You should call for service when you notice:

• Gas Smell: Call immediately if you smell gas near your water heater—this is an emergency that needs professional attention right away.
• Tank Leaking: Water leaking from the tank itself usually means rust has eaten through the metal, and you need a replacement.
• Noise After Flushing: If you've flushed the tank but the sounds continue, something inside has likely failed and needs repair.
• No Hot Water with Strange Sounds: If noises coincide with no hot water, check that your pilot light (gas heaters) is lit. If it won't stay lit or you're uncomfortable relighting it, call a technician.
• Replacing Parts Inside the Tank: Heating elements, thermostats, and relief valves all connect to electricity or gas lines—work that needs someone with experience to do safely.
• Advanced Equipment: Plumbers bring tools most people don't own, like devices that listen for where the sounds start, gauges that measure pressure, and cameras that show heat patterns to find problems hiding inside your tank.

Inspection and Maintenance Steps

A trained technician walks through a few checks to track down your noise problem. During a service call, expect your plumber to look for puddles around the base and check for rust stains or pipes that have worked loose. They'll test your relief valve to make sure it's not stuck or dripping which can cause whistling or create safety risks.

Flushing the water heater tank washes away all that sediment, creating the popping and rumbling. A pressure gauge shows whether your home's water pressure is too high, and if that's the case, they'll install a valve to bring it down. For banging sounds when faucets slam shut, shock absorbers go in near the tank to stop water hammer.

Preventive Measures to Reduce Future Noise

Regular water heater maintenance stops most noise problems before they start. A technician can handle these tasks during routine service calls:

• Annual Tank Flushing: Drain and flush your tank once a year to remove sediment buildup. Flush every six months if you have hard water.
• Annual Anode Rod Inspection: Check your anode rod yearly for corrosion. Replace it when you see several inches of exposed core wire or heavy deterioration-typically every 3-5 years, but potentially sooner depending on water quality.
• Annual T&P Valve Test: Lift the temperature and pressure relief valve lever once a year to ensure it discharges water properly. Schedule professional inspection of this valve every 5 years.
• Pipe Insulation: Insulate hot water pipes to reduce heat loss and prevent banging sounds.
• Thermostat Setting: Keep your water heater at 120°F to prevent excessive sediment buildup while maintaining comfortable hot water.
• Professional Maintenance: Schedule service when you notice persistent problems or if you're uncomfortable performing maintenance yourself.

With over 80 years of water heating experience, A. O. Smith has built a nationwide network of trained local contractors who understand why your water heater might be making noises. They know the difference between sediment that needs flushing, heating elements that need replacing, and pressure issues requiring valve adjustments.

Your technician arrives with specialized tools to diagnose your exact problem—whether it's popping from mineral buildup, whistling from a stuck relief valve, or banging from water hammer. Find an authorized A. O. Smith contractor near you to schedule a diagnostic visit and get your water heater running quietly again.

Think it's time to replace your model? Use our XPERT Residential Water Heater Selector to find the right system for your home's needs.