Some sounds are normal; others signal a problem. Here’s what rattling, buzzing, clicking, grinding and screeching mean on the indoor and outdoor unit — and which ones mean switch it off and call.
Many CausesFrom rattles to grinding
Some UrgentGrinding/screeching = stop & call
Often FixableMounts, debris, fan & service
Which Noises Are Normal?
Some split system sounds are normal: a gentle whoosh of airflow, occasional clicks as the system starts and stops, and a faint trickling or gurgling of refrigerant moving through the lines. Expansion and contraction of the plastic housing can also cause occasional tapping as temperatures change. These are nothing to worry about. It’s the louder, harsher or new noises that warrant attention.
Indoor Unit Noises
Rattling or vibrating — often a loose cover, panel or mounting, or debris caught in the fan. Clicking that won’t stop — can be a relay or fan obstruction. Buzzing — electrical or a vibrating component. Squealing — a worn fan bearing or belt-related issue. A dirty fan can also become noisy and unbalanced. Many indoor noises are resolved by a service that cleans the fan, tightens mounts and clears debris.
Outdoor Unit Noises
The outdoor unit houses the compressor and fan, so it makes more noise. Loud humming or buzzing can be the compressor under strain or an electrical issue. Rattling is often loose panels or fan obstruction. Grinding or screeching suggests a failing fan motor or compressor bearing — these are the urgent ones. A sudden change in the outdoor unit’s sound is worth investigating before a small issue becomes a failure.
Noises That Mean Stop and Call
Turn the system off and call a technician if you hear grinding, screeching, loud banging, or a harsh metallic sound — these point to mechanical failure (fan motor, compressor) that can worsen quickly and cause expensive damage if the system keeps running. A persistent loud electrical buzz is also worth prompt attention. When in doubt, switching off and getting it checked is cheaper than running a failing component to destruction.
Getting It Fixed
A technician will identify the source — cleaning and balancing the fan, tightening or replacing mounts, clearing debris, and checking the compressor and electricals. Many noise complaints are resolved as part of a service. Where a component (fan motor, bearing) is failing, it’s repaired or replaced. Catching a noise early often means a simpler, cheaper fix. See our what a service includes.
Frequently Asked Questions
Why is my split system making a rattling noise?
Rattling is usually mechanical and minor — a loose cover, panel or mounting bracket, or debris (leaves, insects) caught in the fan. On the outdoor unit it can be loose panels or the fan touching something. Rattling is generally fixable by tightening mounts, clearing debris and cleaning the fan, often as part of a service. It’s worth addressing so it doesn’t worsen, but it’s rarely an emergency.
My split system is grinding or screeching — what do I do?
Turn it off and call a technician. Grinding and screeching point to a mechanical problem such as a failing fan motor bearing or compressor issue, and running the system in that state can cause it to fail completely and cost much more to repair. Unlike a harmless rattle, these harsh metallic noises are the ones that warrant stopping the system promptly.
Is it normal for a split system to make clicking or gurgling sounds?
Yes — occasional clicking as the system starts and stops is normal (relays and components engaging), and a faint trickling or gurgling is just refrigerant moving through the lines. Light tapping as the housing expands and contracts with temperature is also normal. These quiet, intermittent sounds are part of normal operation. Persistent, loud or harsh noises are what indicate a problem.
Why is my outdoor unit suddenly louder?
A sudden increase in outdoor-unit noise can be loose panels, debris in the fan, a fan or compressor working harder (sometimes due to dirt or a refrigerant issue), or the early signs of a failing component. Because the outdoor unit contains the compressor, changes in its sound are worth checking before a minor issue becomes a failure. A service can identify and address the cause.
Can servicing fix a noisy split system?
Often, yes. Many noise complaints — rattles, vibration, a noisy or unbalanced fan, debris — are resolved during a service that cleans the fan, tightens mountings and clears obstructions. Where the noise comes from a genuinely failing component like a fan motor or bearing, that part is repaired or replaced. Catching noises early usually means a simpler fix.
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