Technician repairing air conditioner

Modern air conditioning systems are designed to operate silently. Most are fitted with noise dampening material to keep noise levels below 25 decibels, which is equivalent to a whisper — so if your air conditioner makes loud noise when starting, chances are a part or so may be malfunctioning.

Pay attention to the type of noise the air conditioner produces when it starts. An air conditioner can produce a wide range of noises, and each type can be an indicator of a specific issue.

Let’s take a look at the seven most common types of air conditioner noises and what might be the cause for each.

Why Is My Air Conditioner Making a Banging Noise?

The compressor is the most common cause of a banging noise in an AC system when it is starting. It could also be caused by a broken fan motor in your AC unit.

Over the years, the compressor wears down and loses its efficiency. As it nears the end of its lifespan, it may become extremely noisy. In most cases, it is not possible to repair a broken compressor or its components. In this case, you will need to repair the entire system.

On the other hand, you might be able to replace a broken motor. Some manufacturers offer a long-term warranty on the motor and can replace it within the stipulated warranty period. If the warranty period has lapsed, it can be quite costly to replace the motor, and it would be better to replace the entire air conditioner.

Why Is My Air Conditioner Making a Rattling Noise?

You will often hear a rattling noise when internal components of the air conditioner have come apart or are damaged. For example, small parts of the motor or screws are loose or broken.

A rattling noise can also be caused by dirt and debris inside the air conditioner unit. If your unit is located outside or near trees and plants, leaves or sticks might have found their way in.

It can be difficult to pin down the exact cause without disassembling the AC unit. While you can do it on your own as long as the unit is shut off, it is better to have an HVAC specialist inspect and take apart the system.

Why Is My Air Conditioner Making a Squealing or Screeching Noise?

A screeching noise or squealing sounds in an air conditioner unit are primarily caused by issues in the motor. It could be a broken fan motor, worn-out fan bearings, or worn-out or broken belt. The screeching noise can be deafening, necessitating the need to shut down the system.

Furthermore, it can be hazardous to keep operating the HVAC unit. Therefore, shut it down from the main power source and call an HVAC specialist immediately. You may need to replace the motor or the entire air conditioner.

Why Is My Air Conditioner Making a Humming Noise?

Humming noises in an air conditioner are often caused by a defective contactor relay switch. The switch is designed to start the outdoor condenser unit once the thermostat has signaled it. If it is defective, it poses an electrical hazard, and you should not turn the system on until the issue is fully resolved.

Other possible causes of humming sounds are low lubricant levels or bent fin coils. If the lubricant level is low, the humming sound progresses to a grunting noise if you keep running the unit without proper lubrication. Bent fin coils are easy to identify, and you can straighten them yourself using a metallic comb.

Why Is My Air Conditioner Making a Buzzing Noise?

A buzzing sound is caused by loose components that have not detached completely. When the unit is turned on, the loose parts vibrate, producing the buzzing sound you hear. It could also result from dirty condenser coils, loose wires, or a loose motor fan. Whichever the case, you need to have a professional inspect it and recommend repair measures.

Why Is My Air Conditioner Making a Clicking Noise?

It is normal for an air conditioning system to produce clicking sounds when starting or at the end of cooling cycles. However, if the clicking noise becomes continuous, the thermostat may be malfunctioning. This will call for the replacement of the thermostat.

The process of changing a thermostat can be a bit complicated, depending on the thermostat model you choose and may require the services of a licensed contractor.

The clicking sound could also be caused by faulty electrical signals, discharged capacitors, or an obstruction in the AC fan. If the issue is a loss of charge in the capacitor, it will not be able to power the compressor. As such, the entire unit will fail to come on. Rather, it will produce a clicking sound every time you power it on.

If the AC fans in your outdoor unit are obstructed, the unit will run, but there will be a clicking sound near the fan. The air conditioner needs routine maintenance to remove whatever might be obstructing the fan. You can do it yourself by powering off the unit and opening the outer cover. You can then clean the fans.

Why Is My Air Conditioner Making a Hissing Noise?

Several things could cause a hissing noise, including a refrigerant leak, an AC compressor valve leak, or high compressor pressure. If the issue is high compressor pressure, the hissing noise will transform into a shrieking sound after a while.

A refrigerant leak is caused by damage to the refrigerant line. All these possible causes can lead to severe damage to the unit. Therefore, you should power off the entire system and contact a specialist.

Why Is My Air Conditioner Making a Grinding Noise?

You may also hear a grinding noise when turning on your air conditioning unit. A grinding noise is often caused by the pistons that are responsible for compressing the refrigerant gas. When the AC compressor is worn out, you may hear this grinding noise and it may result in an AC compressor replacement or the replacement of your entire AC unit.

Bottom Line

air conditioner makes loud noise when starting
Source: Shutterstock

So, what should you do if you notice that your air conditioner makes loud noise when starting?

It is best to shut down the entire system as soon as you notice any unusual noise, then contact an HVAC specialist to diagnose the issue and advise on the next steps to fix it.

While the noise when your air conditioner is starting may be due to a minor issue or a common air conditioner problem, it could also signal a major issue, leading to severe damage to the unit. It can be difficult to pinpoint the exact cause of the noise. Therefore, leave the diagnosis and repair to experts.

To keep your air conditioner operating in tip-top condition, ensure that a professional maintains it regularly. Also, have an HVAC specialist inspect it every year.