Quick answer
Heat pumps in the Puget Sound normally hum during operation and may whoosh, click, or briefly run louder during defrost cycles in cold weather — but grinding, screeching, banging, or persistent loud clicking usually signals a problem worth professional diagnosis.
- Steady hum, airflow whoosh, and brief defrost sounds are normal.
- Reversing-valve clicks and outdoor 'steam' during defrost are by design.
- Grinding, screeching, banging, or hard repeated clicking is not normal.
- New sounds after winter set-in are worth a quick professional check.
When a new sound appears
Especially after your first winter with a new heat pump, when defrost cycles you've never heard before can be alarming, or when a ductless head starts rattling or buzzing. Being able to tell a routine defrost from a failing bearing saves you an unnecessary panic — and, just as important, helps you catch a genuine problem while it's still a small repair.
Why heat pumps sound different than furnaces
Unlike a furnace that simply fires and blows warm air, a heat pump has an outdoor compressor, a reversing valve, and a defrost cycle, so it makes a wider range of sounds — and it runs year-round. Cold-climate units defrost more frequently than older models by design, which means more of those 'new' winter sounds are completely normal in our marine climate.
How it works
Normal sounds
Expect a steady fan and airflow, occasional defrost mode (the outdoor fan stops, the reversing valve clicks, and you may see steam rising from the outdoor unit as frost melts), and soft expansion-valve clicks as the system adjusts. A gentle hum from the compressor is normal. Cold-climate heat pumps enter defrost more often in our damp winters — that's expected behavior, not a malfunction.
Sounds that mean call a technician
Metal-on-metal grinding, loud squealing from belts or bearings, banging or clanking, repeated hard-start thunks, gurgling refrigerant lines that suggest a low charge, or buzzing that won't stop all warrant service. Indoor units leaking water, or a head that rattles loudly rather than hums, also need attention. These point to mechanical wear, refrigerant issues, or loose components rather than routine operation.
How to describe it when you call
Note when the sound happens (startup, defrost, continuous), what it sounds like (grinding vs clicking vs gurgling), and whether comfort has changed. A clear description helps the technician arrive prepared and often shortens the diagnosis. Recording a short audio clip on your phone is genuinely useful.
Key terms and context
This guide is written for heating & air decisions in the Puget Sound. It uses the same terminology you'll hear from inspectors, technicians, and permit offices.
Ignoring warning sounds
Compressor damage from low refrigerant, or failing fan and blower motors, often announces itself as noise before total shutdown. Acting on a new grinding or screeching sound early can mean a motor or capacitor replacement; ignoring it until the system quits frequently means an emergency call and a much larger repair — sometimes the compressor itself.
Assuming every sound is an emergency
The opposite error is shutting the system down or panicking over a normal defrost. Knowing the routine sounds prevents unnecessary service calls. When in doubt, a quick phone description to a technician can usually tell you whether to keep running or schedule a visit.
How we build this guidance
- Sound guidance drawn from manufacturer O&M manuals and Eco field-technician experience.
- Refrigerant and compressor diagnoses use proper gauges and electrical testing.
- We help you tell routine defrost from a real fault before you spend on a service call.
Methodology: Sound guidance from manufacturer O&M manuals and Eco field-technician input; any new mechanical noise should be evaluated in person.
Last updated: 2026-06-08
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Common questions
Why does my heat pump steam in winter?
During the defrost cycle, the outdoor coil briefly warms to melt accumulated frost, and the resulting vapor looks like steam or smoke for a few minutes. This is completely normal in Puget Sound winters. If the 'steam' is accompanied by a burning smell or persists far longer than a few minutes, shut the system off and call Eco.
Is it normal for the outdoor fan to stop in cold weather?
Yes — during defrost, the outdoor fan pauses while the system reverses to melt frost off the coil, then resumes. You may also hear a distinct click from the reversing valve. This cycle lasts a few minutes and repeats as needed in cold, damp conditions. It's a designed function, not a fault.
My heat pump is louder than it used to be — should I worry?
A gradual or sudden increase in noise is worth investigating, especially if it's grinding, squealing, or banging. It can indicate worn bearings, a failing motor, or loose hardware. Schedule a check — addressing it early usually means a smaller, cheaper repair than waiting for the part to fail completely.
What does gurgling or hissing from the lines mean?
Gurgling or persistent hissing can indicate a refrigerant charge issue or a leak. Refrigerant problems strain the compressor — the most expensive component — so they shouldn't be ignored. A technician with proper gauges can confirm the charge and locate any leak rather than simply topping it off.
Can a rattling ductless head be fixed easily?
Often, yes. Rattles in a ductless head frequently come from a loose cover, a dirty or loose fan, or a mounting that needs tightening — straightforward to correct. Persistent buzzing or grinding, however, may point to a fan motor or bearing issue that needs parts. A quick service visit identifies which it is.