Common Air Conditioner Noises And How To Address Them

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When household appliances like fans, refrigerators, and air conditioners operate, they naturally produce a level of background noise. However, an excessively loud sound when starting an air conditioner typically signals a problem. Such disruptions warrant a closer examination to prevent potential escalation into more significant issues. This comprehensive article from Miller Oil Company will explore common causes and effective solutions for addressing why an air conditioner makes loud noise when starting.

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Air Conditioner Makes Loud Noise When Starting

It’s common for homeowners to notice various loud sounds as their air conditioner kicks on. Each distinct noise can indicate a specific problem requiring attention. Rather than attempting repairs independently, consult with a professional HVAC technician for accurate diagnosis and safe resolution.

Understanding Different Air Conditioner Noises and Their Origins

Here’s a closer look at the everyday unusual noises from air conditioners and their potential causes:

Clanging and Banging Noises

image of residential HVAC units installed outside the house

These sounds typically emanate from the air conditioner’s outdoor unit. A blower motor, which circulates air into your home, can get damaged and create unusual noises. Loose parts may also shift and strike the protective cage, and other causes like fallen debris, thermal expansion, or damper movement should be considered.

Screeching Sounds

When you hear screeching, similar to metal grinding against metal, it often indicates worn fan motor bearings. While not immediately urgent, addressing this issue promptly with an HVAC technician can prevent further damage and ensure the unit’s efficiency.

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Clicking Sounds in the Air Conditioner

Clicking noises often suggest electrical problems within the unit. If you attempt to activate the air conditioner and it fails to start, this indicates an issue. Professional HVAC contractors are best equipped to handle this, focusing on critical components like the capacitor, compressor, and thermostat.

Pulsating Noises from the Cooling System

image of air conditioner damaged fan blades that makes pulsating noise

While a subtle pulsating sound is normal as air moves through the system, a noticeable pulsating from the outdoor unit that’s audible indoors is unusual. Obstructions such as twigs or damaged fan blades within the unit could cause this.

Whirring Sounds in the Air Conditioner

A whirring noise often indicates a mechanical problem within the air conditioner, potentially affecting the indoor and outdoor units. This issue could stem from broken belts, defective blades, worn bearings, or failed fan motors. To prevent further damage, turn off the unit and contact a technician for repairs.

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Buzzing or Humming Noises

Should you notice a humming sound from the outdoor unit, inspect it for trapped debris like flowers, leaves, and branches that can enter through openings. Clearing these obstructions promptly is crucial. Additionally, a buzzing sound may suggest that the fan is deteriorating.

Rattling Sounds in Air Conditioners

baby rattles depicting rattling sound from air conditioner

Rattling in an air conditioner often points to components that have loosened over time due to vibrations. Inspecting and tightening screws and bolts around the unit can sometimes quickly resolve this issue. Additionally, cleaning the coils and replacing the air filter can enhance the unit’s efficiency. For comprehensive care, consider scheduling annual maintenance with an HVAC company.

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Routine Fixes by HVAC Contractors for Noisy Air Conditioners

Learn more about solutions to air conditioning noise issues:

Maintaining and Repairing Coil Fins

ductless air conditioner with exposed coil fins

Ensuring that coil fins are clean and straight is crucial for the performance and efficiency of your air conditioner. Schedule a regular tune-up with an HVAC contractor who can straighten the fins using a fin comb and remove dirt from surrounding areas with a vacuum equipped with a brush attachment.

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Securing Loose Screws

Air conditioners often vibrate during use, loosening screws over time and causing rattling. Regular HVAC maintenance should include tightening these screws to prevent noise and ensure efficient operation.

Clearing Debris from Air Conditioner Blades

HVAC technician checking outfoor unit for debris on blades

Inspect and clean the air conditioner’s cabinet regularly. Removing debris, especially around the fan blades, is straightforward and can significantly boost the unit’s performance.

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Correcting Bent Blades

After cleaning, inspect the blades for any deformities. If uneven, the blades should be carefully bent back into proper alignment. Hiring an HVAC contractor for this task is advisable to ensure it’s done correctly and prevent further damage.

Lubricating the Motor

A screeching sound often indicates the need for motor lubrication. To prevent such issues, regular tune-ups typically include lubrication. During maintenance, technicians use the correct oil and apply it to essential areas, including the oil ports at the base of the fan motor, to eliminate noise and enhance operation.

Steps Homeowners Can Take When Air Conditioner Makes Loud Noise When Starting

next steps written on notebook depicting steps homeowners can take when AC makes loud noise

Learn what steps to take if your air conditioner starts making unusual noises:

Inspect the Outdoor Fan and Unit

First, examine the condenser fan located at the heart of the outdoor unit. Check if it rotates freely and observe whether the blades spin smoothly without signs of imbalance or unexpected contact, which could stem from debris inside the casing. Also, inspect the coils and refrigerant piping. If these components are unfamiliar, it’s safer to defer this task to a professional.

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Replacing HVAC Air Filters

Regularly changing the air filters is essential for maintaining your air conditioner’s efficiency. Clogged filters restrict airflow, causing the unit to work harder and possibly emit a humming noise. It’s recommended that the filters be checked monthly and replaced as necessary to ensure optimal functionality.

Maintaining Your Outdoor Air Conditioning Unit

Miller Oil Company professional HVAC technician attending to AC outdoor unit

The outdoor unit is exposed to environmental elements and can accumulate dirt and debris. For safety, always turn off the unit before starting maintenance. Open the case, remove the top grille, and clear any debris you find. Make sure to secure the case once you’re done.

Testing the Run Capacitor

Once you’ve cleaned the air conditioning unit, restart it to check if the fan operates correctly. If the fan still fails to spin, try manually jumpstarting it with a long stick to push the blade and generate momentum. If this action gets the blades moving, it likely indicates a faulty run capacitor.

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Evaluating the Indoor Air Handler

If the outdoor unit functions correctly, shift your indoor inspection to the air handler. Look for signs of ice buildup or bent coil fins. If present, turn off the power to allow any ice to thaw and the unit to dry thoroughly before powering it back on.

Call an HVAC Company

While homeowners can manage many basic air conditioner maintenance tasks to prevent noise issues, some problems require professional expertise. If the noise persists after you’ve tried all the suggested solutions, it’s time to contact an HVAC professional for assistance.

Preventive Measures for Reducing Air Conditioner Noise

Here are several preventative steps you can do to minimize AC noise:

Install a Noise Barrier

Consider installing a noise-reducing barrier to mitigate air conditioner noise that disrupts daily activities or sleep. Options like sound blankets or noise-reducing fences are effective. Consult with an HVAC contractor to determine the best solution for your needs.

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Maintain Regular HVAC Service

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Ensure your air conditioner receives annual maintenance. Professional technicians can determine and address issues early, preventing them from escalating. Regular expert cleaning also reduces the need for DIY efforts and minimizes the likelihood of disruptive noise from your unit.

Consult an HVAC Expert Promptly

Contact an HVAC contractor when you notice unusual noise from your air conditioner. Addressing these sounds early can prevent them from developing into more significant issues. Early interventions for minor problems are often more cost-effective than fixing severe malfunctions later.


Monitor your air conditioner closely; it often signals its issues through noise. Manufacturers strive to minimize operational noise, familiarizing you with what’s normal for your unit. If you detect any deviations, investigate immediately. Always seek assistance from a qualified HVAC technician for complex issues.

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