Heat pump making noise?
Some heat pump sounds are normal; others signal a problem. Here is what each noise usually means and what to do.
Normal heat pump sounds
A few sounds are expected and harmless: a soft hum or whoosh while running, a click when it starts or stops, and a brief burst of noise and steam during a defrost cycle in winter. Variable-speed units are usually very quiet.
Noises that signal a problem
| Sound | Likely cause |
|---|---|
| Loud buzzing/humming | Failing contactor, loose part, or electrical issue |
| Rattling / vibrating | Loose panel, screws, or debris in the fan |
| Grinding / screeching | Worn fan or compressor motor bearings |
| Hissing | Refrigerant leak or pressure issue |
| Banging / clanking | Loose or failing compressor component |
Quick things to check
- Tighten the outdoor unit's access panel and screws (a common rattle source).
- Clear leaves, twigs or ice from the fan and coil.
- Make sure the unit sits level on its pad.
- If the noise is electrical, grinding, hissing or banging — turn it off and call a pro.
Frequently asked questions
Why is my heat pump humming loudly?
A soft hum is normal, but a loud buzzing hum often means a failing contactor or an electrical/loose-part issue — have it checked.
Is it normal for a heat pump to make noise in winter?
Yes — a burst of noise and steam during the defrost cycle is normal and lasts a few minutes.
When should I worry about heat pump noise?
Hissing (refrigerant), grinding/screeching (bearings) and banging/clanking (compressor) are not normal — shut it off and call a technician.
Related
Sources & further reading
Educational guide, reviewed against US DOE & ENERGY STAR guidance and updated June 2026. Estimates only — not a substitute for a professional assessment or Manual J load calculation.