AC making a loud noise?

Match the sound. Each one points somewhere specific, & two of them mean turn it off.

What does it sound like

Grinding or screeching. A motor bearing, either the fan outside or the blower inside. Turn it off. Running it finishes off the motor.
Buzzing & the outdoor fan isn't spinning. Capacitor. Turn it off, the compressor is cooking.
Buzzing but the compressor & fan are running. Usually the contactor. Usually okay to run until we get there.
Banging on startup. A loose blower wheel or something sitting in the outdoor fan. Turn it off before it breaks something else.
Clicking but nothing starts. A relay or the thermostat. Not dangerous, just not cooling.
Hissing or whistling. Refrigerant leaving or air leaving a duct. Either way it's money leaving.
Loud humming or a hard knock from the outdoor unit. A compressor on its way out sounds like it means it. Turn it off & call.
Rattling. Panel screws, a loose cover, leaves in the condenser. Usually the cheapest thing on this list.

What it usually is

Fan motor bearings

Fourteen years of Florida summers wear out bearings. A screeching outdoor fan or a grinding blower is a motor on its way out. We replace the motor & the capacitor with it, they go together.

Capacitor or contactor

The two parts that fail most. Buzzing is the sound of one of them trying. Either one is a quick fix, & you see the price in writing before we touch it.

Something loose

A blower wheel that slipped, a fan blade that bent, a panel that rattles at startup. Tightened or replaced on the spot.

What it costs to find out

Residential$95$130 after hours

Commercial$125$160 after hours

Regular hours are Mon to Fri, 7am to 5pm. Most noise calls are diagnosed by ear in the first few minutes, then confirmed with the meter. Written price before anything gets fixed.

From the gallery of gross

The buzzing noise, three different units. All three were the capacitor.

See the gallery of gross

Questions people ask

Depends on the sound. Grinding, screeching, banging, or buzzing with no fan: turn it off. Rattling, clicking, or buzzing with the fan going: it can run until we get there.

Older units are loud, that's just what they are. A new one is a lot quieter, but noise alone isn't a reason to replace. A new noise is.

That's the ductwork, not the unit. Whistling is usually an undersized return, popping is the duct expanding, & both are fixable. Ductwork is its own page.

Think comfort. Think Aphex.