# Why is my AC making a weird noise?

**Short answer:** Noises are the AC's vocabulary, and they translate: buzzing is usually electrical, a failing capacitor or contactor. Grinding is motor bearings dying. Hissing can be a refrigerant leak. Banging means something is loose near a spinning blade, and that one earns an immediate shutdown. Clicking once at startup is normal; clicking rapidly without starting is not.

Every technician does the same thing on a noise call: stand at the unit and listen before touching anything, because the sound usually names the suspect. Here is the translation table, so you can listen like we do.

**Buzzing** from the outdoor unit is electricity complaining. The usual sources: a contactor with worn contacts, $220 to $320 flat, or a capacitor on its way out, $189 to $240, sometimes announced by the compressor humming without starting. A unit that buzzes but will not start has usually [lost its capacitor entirely](/answers/why-does-my-capacitor-keep-failing/), which is the most common repair in Kern County.

**Grinding or squealing** is metal asking for mercy, almost always bearings in the condenser fan motor or indoor blower motor. Motors run $540 to $890 flat, and the useful thing about catching a grind early is that a bearing failure caught late takes the motor with it. A squeal at blower startup that fades in seconds is worth mentioning at the next visit; a constant grind is worth a call this week.

**Hissing** deserves respect. At the outdoor unit or along the copper lines it can be [refrigerant escaping](/answers/is-a-refrigerant-top-off-a-scam/), and a leak found by ear is a leak worth fixing promptly, $340 to $890 including the recharge. A brief pressure-equalizing hiss right after shutdown, though, is normal, which is why the timing of the sound matters as much as the sound.

**Banging, clanking, or thumping** is the one that stops the show. Something loose, a fan blade, debris in the unit, a failing compressor mount, is meeting something spinning, and every minute it runs is a minute it can turn a small repair into a big one. Shut the system off at the thermostat and call. This is the noise where waiting is expensive.

**Clicking** is about rhythm. One click when the thermostat calls and one at shutdown is relays doing their job. Rapid clicking while nothing starts is the system trying and failing, usually electrical, and [repeated attempts strain the compressor](/answers/why-does-my-ac-trip-the-breaker/).

**Rattling** is often the cheapest fix on this page: loose panel screws, debris in the cabinet, a duct vibrating against framing. Worth a look before assuming the worst.

The diagnostic is $89, waived when you book the repair, and describing the noise when you call or text genuinely helps: the right parts get on the truck, and most noise calls end the same visit they start.

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