AC Making a Noise It Never Made Before

The sound tells you a great deal about which component is failing — and which noises mean shut it off now.

Worth attention today

Grinding, screeching and loud metallic banging mean switch it off and call. Those noises are metal contacting metal, and the difference between calling now and calling next week is often the difference between a part and a system.

(561) 814-1600 AC Repair

New noises are one of the more useful symptoms in this trade, because the character of the sound narrows the fault down quickly. A rhythmic sound is usually mechanical and rotating. An electrical sound is usually constant. A one-off bang at start-up is usually a component trying and failing to start. And a noise that changes with the fan speed is coming from the blower rather than the compressor.

The thing worth knowing is which sounds mean 'get it looked at' and which mean 'stop running it'. Buzzing, clicking and gurgling are usually the first category. Grinding, screeching and heavy metallic banging are the second — those are bearings, or a fan blade contacting a housing, or something loose inside the compressor, and continuing to run through them is how a repairable fault becomes a replacement.

Describe what it's doing

Tell us the symptom and we'll tell you what it usually is.

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Before you call anyone

Check these first — they cost nothing

Note WHERE the noise is — indoor cabinet or outdoor unit. It halves the diagnosis
Note WHEN it happens — at start-up, continuously, or when the system shuts off
Record it on your phone if you can; it genuinely helps before we arrive
Check the outdoor unit for obvious debris — twigs and palm fronds get into fan blades
Check that the outdoor unit's panels and screws are not loose and rattling
If it is grinding, screeching or banging heavily, switch the system off

Testing the electrical components inside an air conditioning service panel

If the checks above do not resolve it, the causes below need instruments — pressures, temperature split and static pressure — rather than guesswork.

What it usually turns out to be

Screeching or squealing from the indoor unit

Usually blower motor bearings, or a belt on older equipment. It rarely improves on its own and a seized blower means no airflow at all.

Grinding from the outdoor unit

Condenser fan motor bearings, or the fan blade contacting the shroud. Switch it off — this one damages things quickly.

Loud buzzing at the outdoor unit

Typically electrical: a failing contactor or capacitor, or a compressor drawing hard and failing to start. Common precursor to the unit stopping altogether.

Rapid clicking on start-up

A relay or contactor trying repeatedly to close, or a control fault. Short-cycling like this is hard on a compressor.

Banging or clanking from the outdoor unit

Something loose — a fan blade, a mounting, or internal compressor components. The last of those is serious.

Gurgling or bubbling near the indoor unit

Often the condensate drain rather than the refrigerant circuit, though bubbling in the line set can indicate low charge. Worth distinguishing before assuming the worse one.

A rhythmic rattle that changes with fan speed

Debris in the blower wheel, or a wheel that has come out of balance. Usually straightforward once the cabinet is open.

AC Repair (561) 814-1600

AC Making Noise — common questions

Which noises mean stop running it immediately?

Grinding, screeching, and loud metallic banging. All three are metal contacting metal somewhere it should not, and every extra hour of running makes the repair larger. Buzzing and clicking are urgent but not usually damaging in the same way.

My outdoor unit is just loud generally. Is that a fault?

Not necessarily — older units are simply louder, and a unit against a wall or in a corner reflects sound. What matters is change. A unit that has become noticeably louder than it was is telling you something.

There is a bang when it starts and then it runs fine.

Usually a compressor or fan motor struggling to start, most often a failing capacitor. It is a cheap repair now and an expensive one after the compressor has failed trying.

Want someone to just look at it?

Open 24 hours, 7 days a week. Someone answers the phone at 3 AM. Not a machine.

(561) 814-1600