Why Your Air Conditioner Is Making Noise (And How To Fix It)

Apr 11, 2024

Air conditioners became commonplace in American homes in the 1960s, and it's difficult to imagine a world without them. Old and new air conditioning (AC) systems alike are considered essential appliances, no matter if you live in a studio, traditional house, high-rise, or any other type of dwelling. They operate year-round in some places, regulating temperatures and humidity in areas where heat-related deaths were once a real issue. Seeing how often we use these appliances and how hard they work on a daily basis, it's unsurprising that they don't always operate as planned.

Your air conditioner emits all kinds of noises, from muted buzzing to obnoxious clanging. Unfamiliar sounds can come from indoor units, outdoor units, and any other connected technology, such as thermostats, humidifiers, and air purifiers. When strange sounds arise, it often implies an issue with your system. These troubles range in seriousness and danger levels, and it's important that you know how to recognize these noises. Here is what each buzz or clang means, along with how to fix it.

In simplest terms, air conditioners are high-tech fans enclosed in a box. They have two types of fans — indoor blowers and outdoor condenser units — which rotate to circulate and create cool air. These fan systems are installed over vents and push the hot air out while dispersing cold air into your home. These components are subject to wear and tear due to constantly spinning, and the fan blades may bend or break loose over time. They can smack into other parts of the air conditioner as they rotate, which eventually causes more damage to the fans and their nearby components.

Depending on how off-track the fan blades are, you may hear banging, scraping, or rattling coming from the dislodged mechanisms. This sound will be rhythmic in nature as your fans attempt to maintain their programmed speed and rotation. Shut off your AC unit by flipping the main power button or switching off the circuit breaker box, and check your fan blades. They should be identical in shape and evenly positioned. If any of the blades are loose, you can simply tighten or replace loosened screws. However, if they appear to be physically distorted, you should call an HVAC professional to replace them, even though it will cost you.

If you don't see any issues with your spinning fans, they may not be the pieces to blame for your noisy AC. The fan blades are powered by cooler motors, which are electrical systems that can face several issues. Some of the problems you may encounter are that they're improperly installed, incorrectly sized, poorly insulated, or have too much debris buildup. Of course, the motors may just be too old and need replacement.

An AC motor isn't subtle when something is wrong, and you'll hear a loud screeching or squealing sound coming from your unit that is hard to ignore. An AC system has two separate motors; one connected to the outside fan and one hooked up to the indoor fan. If you hear obnoxious squealing from either one, your best course of action is to turn off the appliance and call for an HVAC technician to replace the malfunctioning unit. A faulty outdoor motor can also reportedly make a buzzing sound, which is another indicator that it is out of order. Although motors can be purchased at home improvement stores, you should leave the installation to a professional who can hook them up properly.

An outdoor machine is more susceptible to nature's whims, especially on properties full of trees and landscaping. It's common for thunderstorms and strong winds to break off branches, sending them tumbling through the air. Eventually, one of these fallen twigs can fall between the grill cover wires and end up in your outdoor AC's fan blades. This usually doesn't cause any significant damage. However, if you neglect to remove the debris, the system will damage and overheat over time.

In this scenario, you'll hear clicking, clanging, rattling, or whirring as the outdoor fan smacks into the debris. The sound will vary in pitch and frequency depending on what exactly is stuck inside. Shut off your air conditioner completely before you even think about reaching in to remove the obstruction. Fans whirl at incredibly fast speeds — from 1,800 to 3,450 rotations per minute — and injuries are inevitable if they aren't switched off before you start troubleshooting (via Today's Homeowner). Once you're sure your system is completely off, you can lift the grill top and remove the offending debris.

If you want to avoid future situations like this, you can and should take preventative measures. Make sure the trees and landscaping around your property are trimmed and healthy to prevent breakage during storms. You can also install a mesh-style leaf guard over the unit as an extra safeguard. Keep in mind that the mesh guard won't stop smaller debris from falling inside, meaning your outdoor unit will still need to be cleaned out from time to time.

If you own a car, you know how important it is to add oil to your vehicle every few months. Unsurprisingly, an HVAC appliance requires the same treatment. You don't have to be an engineer to know that lubricant is the key to a well-running system, and without a layer of oil, the joints and connections rub together and create high friction. The lack of a buffer between system pieces leads to eventual mechanical failure or overheating, both of which can lead to pricey repairs on your system.

When your AC motor doesn't have enough oil, you'll hear a low humming sound that indicates the reduced levels. If you ignore this sound and continue running your unit, the low hum will amplify into a grinding noise. The longer you ignore this noise, the louder it will become and the more damage it'll do to your AC system. Adding oil to the motor is simple for people with a mechanically-aligned background. However, if you've never done so before and don't know the difference between the four oil types you can use, it's recommended you call an HVAC professional.

The most notorious of all AC problems are leaking substances. These unintended spills of gas and liquids can refer to several problems with your AC system, as different broken components release excess water, air, or refrigerant into your home. Some of these leaks are more detrimental than others. A water leak damages a house and its belongings, an air leak runs up an electric bill, and a refrigerant leak is the most dangerous of all. It impacts your physical health since the chemicals can be poisonous if breathed in. During these unfortunate events, air or refrigerant is lost through cracks in ductwork or your refrigerant line.

When refrigerant and air leaks occur, they tend to have one thing in common: They emit a high-pitched hiss or whistle where the crack is located. The air duct issue won't put your health at risk, but the freon issue will. Keeping this in mind, you must take the sharp whistle as a warning. Also, listen for gurgling, as refrigerant lines are known to make bubbling noises in the cracked spot where chemicals meet the air. Usually, the issue is that the ducts, lines, or valves have been worn with time, but they can also leak if they've been improperly fitted or attached to your system. No matter how old your system is or how recent your last inspection was, you should call an HVAC specialist to deal with this repair as soon as possible.

Don't forget that your AC unit isn't operating all on its own, and connected devices can also be responsible for the unfamiliar sounds you hear. A thermostat essentially controls your AC unit by detecting indoor temperatures and adjusting your HVAC accordingly. Depending on what the thermostat senses, it'll turn your HVAC fans on and off and adjust cool air output to ensure your home keeps a comfortable temperature.

If you hear a clicking noise every time your AC fans start up or shut down, you aren't going crazy. This is the mechanical sound of your thermostat switching on and off. The only time you should be concerned with the clicking is if it is repetitive. This is usually a sign that your thermostat battery has reached the end of its life and needs replacement. Before you take the drastic route of calling a professional to replace your thermostat, make sure it's not just dirty filters causing the system hiccup. Sometimes dirty filters prevent proper air circulation, which can impede the thermostat's ability to work properly and cause the incessant clicking.

Since the primary function of an air conditioner is to exchange warm and cool air, it's only natural that condensation forms in response. The condensation is a layer of moisture that gathers around the AC coils and is removed via a drain line that leads outside. Over time, the drainage pipe gets clogged with dirt and mold build-up, which causes the condensation to overflow and leak. This trips up the AC system, causing it to shut off randomly because the machinery detects something is wrong.

Aside from the water pooling on the ground, your system will warn you of an impending clog by gurgling and bubbling. This is the sound of excess water sloshing around in the drain pipe because it cannot flow as designed. You can avoid this issue by flushing the pipes with warm water every three months. Some online sources recommend using diluted bleach or vinegar, but these solutions should be used sporadically and only during emergency clogs. They are corrosive to metal and plastic can lead to faster breakdown of your system. The better options are to either call a professional, use a drain snake, or vacuum the drain pipe yourself.

By now, you should be more aware of how important it is to keep your system clear of dirt and debris buildup, because there are even more potential problems in a clogged AC unit. Poor circulation due to clogs can cause evaporator coils to freeze up, which is a big problem considering the coils are responsible for the final step in the heat exchange process (they produce the cold air for your home). Ironically, when these systems get encased in ice and freeze over, air is unable to circulate and causes the system to overheat.

You'll know your evaporator coils are frozen when your indoor system emits a constant buzz. This buzzing is the sound of ice-encased coils overworking themselves. To stop the vibrations, you'll have to thaw out your system by shutting it down and letting the ice melt. Replace the dirty air filter, which is usually the culprit behind this issue. When you start up your system again, it should be back up and running normally. However, if the coils freeze over again, there could be another internal issue, and you may need to seek professional assistance.

If you live in a newer house, townhome, or condominium building, you're probably lucky enough to have a newer air conditioning model. These models are engineered to make less noise during everyday operations. In contrast, people who live in vintage homes with older units aren't so lucky. Most older systems have fans that blow at full force, with no additional engineering to muffle the loudly spinning blades. Every time they power on, you'll hear a loud whirring as they start up and run, which can be disruptive for people who work from home or have trouble sleeping. Seeing as there's no problem with these air conditioners, you may think there's nothing you can do except replace the system. While you can replace the entire unit, this is not your only option.

There are special innovations on the market, which are known as sound blankets. Sound blankets are insulated rubber pieces that can be installed over a compressor to reduce noise by 30% to 50%. If you have the yard space, you can also build a plywood fence around your AC unit to help contain the noisiness. You can also invest in a portable mini fence designed specifically for this purpose, dubbed the "Quiet Fence." Just keep in mind that any temporary or permanent barricades should be at least three feet away from the unit to allow proper airflow.