A water heater is not completely silent. Metal expands, water moves through piping, electric elements can hum, and gas burners cycle on and off. The better question is what sound you hear, when it happens, and whether it is new.
Soft clicks and humming can be normal
Clicks at the beginning or end of a cycle can come from controls or expanding piping. A low hum on an electric heater may simply be the heating elements operating.
If the sound is mild, familiar, and not accompanied by leaks, burning odors, or poor performance, it usually does not require immediate repair.
Rumbling and popping often point to sediment
Minerals can settle at the bottom of a storage tank. Water trapped around those deposits can make popping or rumbling sounds as it heats.
Rheem identifies sediment as a common cause of those noises and recommends periodic maintenance. If an older tank has never been flushed, however, do not aggressively drain it without considering the condition of the valve and tank.
A high-pitched whistle is more about flow
Whistling can occur when water is forced through a restricted opening. A partially closed valve, mineral buildup, or a pressure problem can all be possibilities.
Do not start adjusting valves based on sound alone. Verify only accessible controls you understand, and have system pressure checked if the noise persists.
Hissing with moisture deserves caution
If hissing or sizzling appears along with water, unusual condensation, or a damp area, moisture may be contacting a hot surface. That deserves prompt attention on both gas and electric equipment.
Do not remove covers while the heater is energized. Burning smells, water near electrical connections, or abnormal burner behavior are reasons to shut the appliance down safely and call for service.
The pipes may be the real source
A sharp bang when a faucet or appliance valve closes can be water hammer: moving water stops suddenly and shakes the piping. Because the vibration travels through the plumbing, it can sound as if the heater caused it.
Notice whether the noise happens when a washer, dishwasher, or faucet shuts off rather than during heating. That timing can redirect the diagnosis.
Tankless heaters have different operating sounds
Tankless units may include fans, ignition systems, and rapid internal water flow. Scale in the heat exchanger can also change their sound and flow. Their maintenance procedure is different from flushing the bottom of a storage tank.
When noise becomes a service issue
Get help if the sound suddenly becomes loud, is paired with a leak, hot water performance changes, a breaker trips, or you smell gas or electrical burning.
Recording the sound and noting exactly when it happens can be more useful than calling it a “weird noise.” Timing—startup, active heating, fixture shutoff, or constant noise—often tells you more than loudness alone.
Sources
- Rheem — The Ultimate Guide to Water Heater Noises — Manufacturer guidance distinguishing normal sounds from sediment, pressure, flow, and leak-related noises.