A heat pump water heater normally makes fan and compressor sound while heating. Judge a new noise by its timing, operating mode and changes from normal, rather than treating every hum as tank sediment. A sudden scraping, escalating vibration or another alarm needs inspection. Keep required air openings clear and avoid opening the heat pump housing.
Match the sound to the operating mode
Look at the selected mode and display without removing covers. A hybrid heater can use its heat pump, its electric elements or both, depending on its controls and demand. Fan sound may therefore come and go even while the tank stays hot. ENERGY STAR explains that the appliance moves heat from surrounding air rather than relying only on electric resistance heating.
The cited Rheem manual says new electrical appliances make some sound and directs increasing excessive hissing or singing to an installer or plumbing contractor. Its specification sheet gives a sound rating for the listed model family. That brochure figure is not a universal threshold for every heater, every room or every noise diagnosis.
Check outside the heater first
Make sure stored objects are not resting against the cabinet or blocking air openings. Inspect only the owner-serviceable filter using its care instructions. A heat pump water heater filter cleaning is different from removing the fan guard or reaching into the compressor compartment.
Write down when the sound starts, how long it lasts and whether the display reports an alarm. A recording made from a safe distance can help the service technician compare the sound with normal operation. Do not move the appliance, loosen its supports or bend connected piping to chase a vibration. Installation changes can affect water connections and drainage.
Before enclosing the heater to reduce sound, review its closet airflow and permitted ducting. A noise enclosure must not obstruct the manufacturer's required air or service access.
Know when noise deserves service
A new scraping sound, significant vibration, repeated fault messages or a burning smell requires a closer look. Stop using an appliance with an evident electrical hazard and arrange qualified service; do not open panels or repeatedly reset a tripping breaker. Fan, compressor and electrical tests require the correct equipment and model instructions.
For the appliance's installation needs, see what a hybrid water heater is. A popping sound from the storage tank has a different investigation: water heater popping and rumbling explains sediment and other tank-related sounds. No single noise proves the tank needs replacement.