My Air Conditioner Makes a Loud Noise When Starting

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Updated August 12, 2022

Even the best air conditioning units occasionally make strange noises when they start. A loud buzz or rattling noise might signify underlying issues with your air conditioning system. While some air conditioner noises require professional repair services, you can diagnose simple problems with this guide. Stick around to learn, “Why does my air conditioner make a loud noise when it turns on?”


  • Your AC should not make loud noises on startup, which usually indicates an internal defect.
  • A faulty compressor motor is the most common and expensive cause of loud AC sounds during startup.
  • Loose components like the fan assembly and motors can knock against internal hardware and outdoor debris.

Why Does My AC Unit Make a Loud Sound On Startup?

If your air conditioner makes an obnoxious sound on startup, you may have an electrical issue or loose components inside the unit. Whether you have a loud buzzing noise that won’t stop or a continuous clicking noise, it is a bad sign for your system.

Insider Tip

Making routine maintenance calls is the best way to ensure the longevity of your air conditioning system.

You may need an HVAC professional to solve these AC issues, especially if the unit keeps turning off on its own.

Electrical Connection Issue

A failing compressor motor will cause loud noises on startup, which is a major AC issue. If you notice reduced cooling power or frozen coils, your compressor motor is likely causing these loud noises.

If this clicking noise persists past startup, you may have a busted capacitor or thermostat. Lastly, check for a refrigerant leak or dirty air filters, as this can harm the electrical system.

Faulty Motor

A bad fan motor bearing will cause a harsh grinding sound when you start the AC. An unlubricated motor sometimes makes this noise until the system warms up a bit. Everything from the blower motor to the condenser fan motor can wear down over time, and they require professional service to replace.

Dirty Outdoor Unit

Dirt and debris will enter the outdoor condenser unit over time. Obstructions and damage to the fan cage cause the blower wheel to knock against the fan blade. In addition, loose fan blades can knock around inside the unit, creating bothersome air conditioning noises and cooling issues.


Do not attempt an AC repair or service activity without disconnecting the electrical components from the circuit breaker.

Clicking Sounds from Air Ducts

If you have sheet metal ducts, you may hear creaking and rattling noises from your air vents. These metal ducts will creak as the internal pressure and temperature fluctuations cause them to expand and contract.

STAT: A 2020 US EIA (Energy Information Agency) survey shows that 93% of homes built between 2010 and 2020 use air conditioning. (source)

Why Does My Air Conditioner Make a Loud Noise When It Turns On FAQs

How can I reduce AC noise inside my home?

If an experienced technician confirms that the AC's annoying noises aren't an issue, you can muffle the sound. You can place a sound blanket around the compressor motor, but you should disconnect the unit before opening it up.

Should I repair or replace my AC unit?

You should only invest in air conditioner repair services if your AC unit is under ten years old or costs less than 50% of a new model. EnergyStar recommends a complete replacement every 10 to 15 years, so you should install a new central air conditioner if your old unit has a severe issue.

How much does it cost to replace an AC compressor?

A broken compressor replacement is one of the most expensive repairs to an AC system. It costs between $800 and $3000 to replace a faulty compressor, and most experts recommend an air conditioner replacement.
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