11 Common Reasons Your AC Unit Is Making Loud Noises

When an air conditioner works well, you will not even notice its presence. But when you hear squealing, rattling, banging, or other unwelcome sounds coming from your air conditioner, it is likely time for a repair. Knowing how to face these issues will keep your AC problems from becoming a hot mess. As with any machine, keeping up with service and maintenance is always a good idea for preventing breakdowns.

1. Buzzing

If there is persistent buzzing coming from your outside HVAC unit, it is a good indicator of a refrigerant leak or that your unit is freezing up from too much usage. Turn off the air conditioner for a few hours and then start it up again. If this happens a lot, your unit needs repair.

Buzzing can also mean that your condenser fan is not working. You will know this is the problem if your inside fan runs and you hear the buzzing noise coming from the outside unit. Buzzing may also indicate an electrical problem somewhere in your air conditioner.

How to Fix It

If the indoor fan is running but a buzzing emanates from the outdoor unit, inspect the condenser fan for obstructions or damage. Clear any debris and assess the fan's condition. If you suspect electrical damage, check the system's electrical components, such as wiring and capacitors, for obvious signs of damage. 

For any concerns beyond your expertise, call a qualified HVAC technician to ensure thorough diagnosis and proper resolution.

2. Squealing and Screeching

If you hear a squealing or screeching noise coming from your air conditioner (think nails on a chalkboard or fork scratching a porcelain plate), it is caused by moving parts in your AC unit wearing out and breaking. For example, the belt may need replacement, or the motor bearings could be damaged, which will cause the motor to be off-center, hence the screeching.

Another reason these noises happen is that your motor needs lubrication. Failure to lubricate the AC unit's motor can lead to increased friction and wear, potentially resulting in AC overheating, component damage, and system failure.

How to Fix It

Repairing and replacing belts and motor bearings before they stop working altogether will prevent your HVAC from shutting down. Maintenance is the most important thing you can do to keep these parts in good shape. 

If you suspect the issue is lack of lubrication, make sure to use the correct type of oil (either mineral or synthetic) if you choose to do this yourself. The oil you use should not have any detergent in it, and common oils used around the house, like WD-40, are too light for this issue.

3. Rattling

A rattling sound coming from your AC unit could mean that a panel or door is loose or a component has come loose inside the unit. Additionally, there could be debris caught in the unit or damage to the motor itself.

How to Fix It

• A part has come loose: Turn off power to your AC unit. This needs to be repaired by a pro before the part breaks or disconnects completely.

• The motor is damaged: If the motor appears to be damaged, have a professional replace it.

• The panels or doors are loose: Check if the panels or doors outside your unit are firmly attached. Tighten any loose screws.

• Debris is caught in your AC: There may be some twigs or other material caught in the mechanism. Call a pro for a thorough cleaning. 

4. Thumping

It is normal to hear a thumping noise when your air conditioner powers down, but continuous thumping means something is not working correctly. Thumping can occur inside your house when the filter hits the return grille (the piece that covers the duct and filter) or when the blower fan has come loose. Thumping can also indicate a broken seal or hole in the ductwork. 

How to Fix It

If you hear thumping from outside, your compressor springs may be broken, or the fan may be hitting metal. If you hear thumping repeatedly and it’s getting louder, it may be time to contact a local HVAC pro to take a look.

5. Thwapping

If you hear a "thwapping" sound, similar to playing cards on bicycle spokes, something may be stuck in the blower blades or touching the blower from inside the unit. The issue is not severe, but it could cause the belt or motor to wear out more quickly than it should.

How to Fix It

To address the thwapping sound in your air conditioner, inspect the blower blades for any obstructions or foreign objects that may be causing the noise. Clearing any debris or removing the obstruction from the blower will help alleviate the issue and prevent premature wear on the belt and motor. Regular maintenance, including cleaning and inspecting the blower assembly, is essential to prevent recurring issues with obstructions. 

6. Repeated Clicking

Repeated clicking can be caused by any of the following:

• The relay process: A repetitive clicking noise in your HVAC means there is a problem in the relay process in the thermostat that regulates air temperature.

• An electrical problem: Clicking can indicate an electrical problem connected to the HVAC, which causes the relay to stop working properly.

• The contactor: The connection between the thermostat and the compressor unit, known as the contactor, may be damaged and need replacement. 

How to Fix It

These problems should be fixed by a local professional technician. Attempting to fix electrical or relay-related issues without proper knowledge and training can be risky and may lead to further damage or injury. Professionals have the necessary tools and experience to safely navigate complex HVAC systems, troubleshoot issues effectively, and perform repairs with precision. 

By entrusting the repair process to a skilled technician, you can have peace of mind knowing that your HVAC system will be restored to optimal working condition, minimizing the risk of future malfunctions or safety hazards.

7. Banging

When there’s a loud banging as your unit runs, it means something is broken and needs repair. For example, you may have a damaged piston pin or connecting rod. Banging can also mean you need AC compressor replacement. You should stop using the unit until it is repaired or replaced.

How to Fix It

Stop using the system immediately to prevent further damage. The banging may indicate serious issues, and continuing to operate the unit in this condition could exacerbate the problem and potentially lead to more extensive and costly repairs.

Promptly schedule a professional inspection and repair service. A qualified technician can diagnose the specific problem, whether it's a damaged piston pin, connecting rod, or compressor issue, and make any necessary repairs. AC compressor replacement costs $1,200 on average.

8. Grinding

A grinding sound from your AC often indicates an issue with vital parts, which could be:

• Damaged blower fan bearing or blade

• Damaged AC compressor valve

• Damaged condenser fan bearings

How to Fix It

Turn off the unit to prevent additional wear and tear. Then, carefully inspect the blower fan, compressor valve, and condenser fan for any signs of damage or obstruction. Clean out any debris that may be causing the grinding noise and tighten any loose components. 

If you're comfortable with it, you can attempt to repair or replace damaged parts following the manufacturer’s guidelines. However, if you're unsure or uncomfortable with DIY repairs, seek assistance from a professional HVAC technician to ensure the problem is properly addressed and your AC is back to optimal performance. Depending on the part, you could pay anywhere from $100 to $550 to replace AC blowers and fans.

9. Dripping

As your AC cools, it pulls moisture from the air and into the drip pan. A dripping sound suggests that the condensation (or moisture) is not draining properly. This may also appear as condensation on your AC. 

How to Fix It

Check the drain tube in the drip pan for blockages that might prevent water from flowing out of the unit. If it is dirty, use compressed air or vinegar to remove the clog and get water flowing again. 

10. Whistling

A high-pitched whistling noise suggests something is blocking airflow in your ducts or supply vents. Ensure the vents have enough space to work, with no furniture, dust, or debris blocking them, then move on to your ducts. 

How to Fix It

To remedy a high-pitched whistling noise in your ducts or supply vents, begin by examining the air filters. Replace any dirty AC filters with clean ones to restore proper airflow. Next, inspect the ductwork for any leaks or gaps where air might be escaping. Use duct tape or mastic sealant to seal them, ensuring efficient airflow throughout the system. You may also want to consider installing dampers in the ductwork to regulate airflow and reduce noise levels. 

Blockages and improper installation block airflow, which produces a whistling noise. Call a ductwork contractor to inspect your ducts for blockages and the proper configuration. Budget $250 to $500 for the cost to clean your air ducts.

11. Hissing

When refrigerant leaks in your air handler, it can produce a hissing sound. You should address leaks immediately, as refrigerant is harmful to the environment. 

How to Fix It

Don’t attempt to fix refrigerant issues yourself. Refrigerants are dangerous to work with, especially if you don’t have the proper safety equipment. Call a pro immediately if you think you have a refrigerant leak. Your HVAC pro will refill the refrigerant, find the source of the leak, and repair it. R-22 refrigerant costs $50 to $250 per pound. 

How to Prevent a Noisy HVAC System

Having an operable air conditioner is not just nice to have for our own comfort. In some cases, it can be a lifesaver. As we experience more extreme weather conditions, an air conditioner helps keep us cool. If the air conditioner sound is noisy or loud, it is important to have a professional find the cause of the noise. An HVAC system that runs well is more efficient, too.

There are some ways you can prevent a noisy HVAC system.

Schedule Regular Maintenance

Regular maintenance can help prevent many common HVAC noises, increase efficiency, and save money in the long run. HVAC maintenance costs can be reasonable, especially if they detect issues that can be resolved before they become true emergencies.  

A professional can assist with identifying the causes of noisy air vents, furnace noises, and other types of loud and unwelcome noises. Experts recommend having your HVAC system serviced twice a year. To make it easier to remember, schedule an air conditioner tune-up at the end of spring and fall. 

Add Soundproofing

Even if your AC unit works well, the air conditioner sound may be louder than you would like. You may be seeking ways to quiet a noisy AC unit. In this case, you may want to consider soundproofing your unit. Some ideas include:

• Use a sound blanket: This works by covering the air compressor, which is the noisiest part of an air conditioner. 

• Strategically place plants or fencing: Consider putting plants, shrubbery, or fencing around the perimeter of your air conditioning unit. Some air conditioners make a humming noise. These items can serve as a noise barrier, but be sure to leave enough space for your HVAC to circulate air. 

• Move your AC unit to a better location: This may not be an immediate option, but if or when it needs to be upgraded, consider moving to a better spot that is not as close to any windows. 

If you hear any unusual air conditioner noise, whether your AC is buzzing or just too loud, you will want to hire a local professional HVAC contractor to assist with air conditioner troubleshooting. Malfunctioning parts can become dangerous if action is not taken immediately. Regular service and ongoing maintenance can avoid costly emergencies, as well as make your appliance work more efficiently in the short and long term.