Heat pumps run far more hours than an AC ever did — heating and cooling, all year — so owners hear more of their repertoire and worry more about it. A good share of "strange noise" calls end with us certifying the sound as factory-installed. Here's the by-ear field guide from thousands of driveway listening sessions.
Sounds that are just heat pump life
The defrost whoosh-hiss: every so often in cold weather the unit pauses, makes a pronounced whoosh (the reversing valve flipping), hisses, steams dramatically, then resumes. Pure design. Gurgling and soft boiling in the lines at start and stop — refrigerant equalizing. A deeper hum on frigid mornings as the compressor works harder, and on inverter models a rising-falling pitch as the unit modulates — that variable drone is efficiency, not distress.
Sounds with a work order attached
Metallic scraping or ticking in time with the fan: blades hitting ice (see our icing guide) or a fan going off-center — shut it down before blades meet coil. A rising scream or dry screech: fan motor bearings dying; the motor is replaceable now, or the motor-plus-cooked-capacitor is replaceable later. Hard buzzing with no start, or rapid clicking: the capacitor/contactor duo auditioning for our other articles. A knock or rattle from deep in the compressor at start/stop that's grown over months: internal mounts or valves wearing — this one wants a professional ear soon, because compressors telegraph before they fail. Panel buzz and cabinet rattle: genuinely trivial — loose screws and vibration — but worth fixing because a panel vibrating against a line set can wear a refrigerant leak over years.
The one worth a same-day call
A loud mechanical noise followed by silence — the unit protected itself and stopped. Don't cycle it repeatedly to "see if it clears"; whatever stopped it is still in there, and restarts under fault are how small failures recruit expensive ones.
Our approach
Describe the sound on the phone (or send a video — genuinely helpful) and we'll often narrow it before arriving. On site: listen, isolate with the fan and compressor separated, meter the suspects, fixed quote. Most noise repairs are motors, mounts and hardware — the affordable end of heat pump work when caught at the noise stage rather than the silence stage.
