Why is my HVAC System Noisy?

Posted on March 14th, 2018 by carrolladmin

Before you read this article, please make sure you call us if your HVAC is makes any noise you don’t recognize.

HVAC noises coming from a large heating and cooling unit.


The majority of our residential customers have central forced air heating and cooling, and one of two heating ventilation and air conditioning (HVAC) equipment arrangements. The first is an electric heat pump that handles both heating and cooling functions. This is the most common HVAC system set up in newer homes. The second configuration is a furnace and air conditioner, each separately heating or cooling.

The best system for any home depends on the cost and efficiency of the equipment, yearly energy use, availability of energy sources, and the local cost for fuels like gas and oil. With that said, in most homes, it doesn’t matter so much the type of equipment. As long as it’s sized and installed properly for the house, it should cost-effectively provide indoor comfort.

Know your HVAC System

Do you know what types of equipment make up your home’s HVAC system? If not, you should familiarize yourself. It’s a good idea to understand the location and basics of your equipment if you ever need to troubleshoot an issue before calling a professional. 

Most HVAC systems are fairly reliable as long as they aren’t overdue for a replacement or lack routine preventative maintenance. However, whether it’s during heating or cooling season, problems do occur with no rhyme or reason. HVAC systems can experience many issues, like blown fuses, refrigerant leak, loose parts, worn condenser coils, and damaged thermostats

Related: Common issues with aging equipment

At Carroll Plumbing & Heating Inc., our technicians have seen it all and fixed it all, so none of these problems are tricky repairs for us—if your system isn’t working correctly, just give us a call!

Noisy Operation is Not Something to Ignore

One of the most common complaints we get from customers is in regards to a noisy HVAC system. It’s not out of the ordinary for a customer to tell us that their system has been making strange noises for a while, but they thought nothing of it. Knowing the difference between the normal noises from an unusual noise that suggests a problem can be difficult. This is why we encourage homeowners to understand their equipment, including how it sounds when it’s working correctly.

Some Noise Isn’t Cause for Alarm

One of the most common noises you’ll hear from your HVAC system is the quiet, continual hum of properly functioning equipment. When the system runs, you may hear the motor of the indoor unit in operation, depending on where it’s installed. The outdoor unit includes a fan and a motor, which will most certainly make more noise than indoor equipment.  

It’s also typical for a quiet swooshing sound to come from registers as air rushes through the vents.  

Lastly, a squeal or thump when the system cycles on and off isn’t cause for alarm, but it is an indicator you’re due for a tune-up.

Related: How important is preventative maintenance?

Identifying Unusual Noises

Indoor units – whether the air handler or furnace is reasonably typical complaints when it comes to noise. In many cases, it’s caused by a bad belt or bearing in the blower motor. Unusually noisy motors inside air handlers and furnaces make squealing, screeching, rattling, and/or banging noises when the equipment malfunctions. In most cases, these are inexpensive repairs—adding lubricant, tightening parts, and replacing belts. 

If you know how, you can do it yourself, or give us a call to come out and complete the maintenance needed. 

If you hear a clicking sound inside your home, it’s likely not your air handler or furnace, rather the thermostat. There is an audible click signifying communication between the thermostat and the capacitors when it’s time to activate it. Repeated clicking means there is a defective relay causing the system to timeout and fail when starting up. You should contact an HVAC specialist to complete the repair. 

Outdoor unit – regardless of a heat pump or air conditioner, a sudden loud rattle is usually due to a branch or other type of debris stuck inside the exhaust fan.  

Although there is a grate to protect against objects obstructing your fan, small twigs and debris can make its way inside. If you suspect something is stuck, immediately turn off power to the exterior unit and see if you notice any obstruction.

If you see bent metal, damage to moving parts, or anything else that doesn’t seem right, contact Carroll Plumbing & Heating Inc.  

Vents & registers – a soft rush of air is typical, but a higher noise level is cause for concern.  

An audible hiss could indicate damage to coolant lines, a coolant leak, or improperly sealed ductwork. More commonly, customers complain that air vents and registers make a high-pitched, vibrating type of sound. This can be caused by a lack of return air, which can occur because too many vents are closed off, or furniture is obstructing airflow. It’s also possible a more significant issue exists—undersized or improperly installed ductwork.

More Common HVAC Noises

Thumbing or clanking 

To hear these sounds means you could have a problem with your blower assembly. We recommend you turn off your HVAC system and call a professional to complete a diagnostic.


When you hear a popping sound as you turn your system on and off, it’s usually not a sign of problems brewing. You can rest assured that ‘s just the ductwork expanding. 


A few culprits could cause a buzzing sound coming from your HVAC system. It could be simple like a few loose parts in your unit, or your motor could be going out. You want to schedule a diagnostic to determine the cause of the buzzing sound. 

HVAC systems can produce a wide range of noises—many are normal, but others are not. It’s always best to err on the side of caution when you suspect something isn’t right with your HVAC system because a minor problem can quickly turn into an expensive repair.

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