Heat pump noises explained: what’s normal and what’s urgent

If your air source heat pump has started making new or louder sounds, it can be worrying. The good news is that many noises are completely normal, while others are your system’s way of asking for a professional check-up.

Getting familiar with normal heat pump sounds

Heat pumps are not silent, but they should be steady and predictable. Learning the usual sounds your system makes will help you spot changes early.

Most modern outdoor units produce a gentle background hum along with occasional airflow and valve noises. Sudden, sharp or metallic sounds, or noise that changes quickly, are more likely to need attention.

• Listen regularly when the system starts, runs and stops

• Note changes in loudness, tone or vibration

• Compare indoors vs outdoors to pinpoint the source

• Check at night when background noise is lower

Whooshing noise during defrost

What it can mean

A sudden whoosh or rush of air during cold weather is usually the unit switching into defrost mode. This is part of normal operation as it clears ice from the outdoor coil.

What is normal

It is normal to hear a louder airflow noise plus a change in fan speed for a few minutes. You might see steam rising from the unit and the indoor radiators may briefly feel cooler.

What to check safely

Stand back and visually check there is no heavy ice build-up around the outdoor unit casing or grille. Make sure leaves, snow or debris are not blocking the air intake or discharge.

When to call an engineer

If defrost cycles are extremely frequent, very loud, or ice is not clearing properly, contact an engineer. Persistent icing can reduce efficiency and may damage components if left unresolved.

Clicking and relay sounds

What it can mean

Soft clicking is usually electrical relays and valves opening and closing as the system starts, stops or switches modes. Occasional clicks are expected in all seasons.

What is normal

Single or short bursts of clicks at start-up, shut-down or when the thermostat calls for heat are generally fine. These should not be excessively loud or continuous.

What to check safely

Indoors, listen near the consumer unit and the heat pump controls to understand where the click is coming from. Check that the room thermostat or controller is set correctly and not constantly cycling the system on and off.

When to call an engineer

If you hear rapid, repeated clicking, or the system struggles to start, book a diagnostic visit. This can point to control issues or failing components that are best dealt with early.

Low humming from the outdoor unit

What it can mean

A steady hum is the sound of the compressor and fan running. This is the main operating noise and should be fairly constant at a given output level.

What is normal

A gentle, even hum that does not pulse or buzz sharply is usually fine. You may notice it more at night when surrounding noise drops.

What to check safely

Check that the unit is sitting level and that all access panels appear properly closed. Look for anything leaning on the casing, such as gardening tools or loose pipe lagging, that could resonate.

When to call an engineer

If the hum turns into a strong buzz, becomes significantly louder over time, or you feel harsh vibration through nearby walls, have an engineer assess the compressor and mounting.

Gurgling or trickling sounds

What it can mean

Gurgling is often refrigerant or water moving through the pipework. It can be more noticeable during start-up or when the system modulates output.

What is normal

Light gurgling or trickling that comes and goes, particularly close to the indoor unit or cylinder, can be normal. It should not be extremely loud or continuous.

What to check safely

Check that condensate and drain pipes are not kinked or blocked where you can see them. Indoors, ensure any visible heating pipes are properly insulated and not knocking against walls or other pipes.

When to call an engineer

If gurgling is very loud, accompanied by poor heating performance, or you suspect air in the system, seek professional help. The system may need bleeding, balancing or refrigerant checks.

Rattling from unit feet or base

What it can mean

Rattling or chattering at the base of the unit often points to loose fixings, worn feet or the heat pump vibrating against its support frame or slab.

What is normal

There should be no sharp rattles, even when the fan starts or stops. A correctly installed heat pump should sit firmly, without rocking.

What to check safely

Look at the feet or brackets and check if any rubber pads are missing, perished or out of place. Make sure there are no stones, sticks or loose items trapped between the unit and its base.

When to call an engineer

If the unit visibly shakes, or rattling is heard indoors, an engineer should refit or upgrade the mounting. They can add suitable rubber isolation pads or adjust fixings without stressing the pipework.

Vibrating pipework and indoor noise

What it can mean

Vibration can travel along metal pipework into the building fabric, causing a humming or buzzing in nearby rooms. This is often an installation and support issue rather than a fault with the heat pump itself.

What is normal

A faint background sound close to the indoor pipework can be acceptable. However, you should not hear strong buzzing through walls, floors or ceilings.

What to check safely

Where exposed, look for pipe clips that are loose or missing padding. Check that pipes are not tightly wedged against plasterboard, joists or brickwork, which can amplify vibration.

• Gently feel nearby walls for strong vibration

• Note the rooms and times when noise is worst

• Take a short recording to show your engineer

When to call an engineer

If vibration is disturbing sleep or clearly audible in living spaces, an engineer can re-clip pipework, fit cushioning and adjust compressor settings where appropriate.

High-pitched whine or squeal

What it can mean

A noticeable high-pitched tone may come from the fan motor, bearings, or sometimes the refrigerant circuit at certain pressures. This sound is more likely to need prompt attention.

What is normal

Very faint, occasional tones at close range can be normal. Anything piercing, continuous or audible from inside the house or at the property boundary is not.

What to check safely

Walk around the unit and note whether the whine changes with fan speed or load. Check that nothing has entered the fan guard and that the grille is not bent into the blades.

When to call an engineer

If the high-pitched noise is new, worsening or present most of the time, arrange a diagnostic visit. Early intervention can prevent further wear on motors or other components.

Positioning, clearances and vibration isolation

Good siting makes a big difference to how loud a heat pump seems. Ideally, the outdoor unit should have clear space around it so air can flow freely and sound is not bouncing straight off hard walls.

Mounting on a solid slab or wall brackets with suitable rubber isolation helps absorb vibration. Keeping some distance from bedroom windows and neighbouring properties reduces disturbance, especially at night in quieter areas like Horsham, Pulborough and across West Sussex.

Neighbour concerns and keeping peace

In quieter streets, even normal heat pump noise can feel intrusive, especially for neighbours. A local example would be a compact garden in Billingshurst where sound reflects between fences and walls.

Simple steps such as checking operating schedules, using night-time setback settings and adding acoustic fencing or planting can reduce perceived noise. A well-maintained, correctly sited system is usually very acceptable in residential areas.