When you hear these noises coming from your HVAC, it's time to call a pro
A functioning HVAC works so well, you won’t even notice it’s there. So when you hear a squealing, rattling, banging, or other unwelcome sounds, it's time for a repair.
Knowing how to face these issues will keep your AC problems from becoming a hot mess. And, as with any machine, keeping up with service and maintenance is always a good idea for preventing breakdowns.
1. Squealing and Screeching
If you hear a squealing or screeching noise (think nails on a chalkboard or a fork scratching on a porcelain plate) coming from your air conditioner, it's caused by moving parts in your AC unit wearing out and breaking. For example, the belt may need replacement. Or, the motor bearings may be damaged, which will cause the motor to be off-center—thus the screeching.
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.
Another reason these noises happen is that your motor needs lubrication. Make sure to use the correct type of oil (either a mineral or synthetic) if you choose to do this yourself. The oil you use shouldn't have any detergent in it, and common oils used around the house, like WD-40, are too light for this issue.
A rattling sound coming from your AC unit could mean:
A part has come loose: Turn off the power to your 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, leave it to a professional to replace it
The panels or doors are loose: Check if the panels and 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
It's 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.
If you hear thumping from outside, your compressor springs may be broken, or the fan is 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.
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. This issue is not severe, but it could cause the belt or motor to wear out more quickly than it should.
5. Repeated Clicking
Repeated clicking can be caused by:
The relay process: A repetitive clicking noise in your HVAC means there's a problem in the relay process in the thermostat that regulates the 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 contactor, the connection between the thermostat and the compressor unit, may be damaged and need replacement
These problems should be fixed by a local professional technician.
If there is persistent buzzing coming from your outside HVAC unit, it's a good indicator that there’s 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'll 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.
When there’s a loud banging as your unit runs, it’s broken and needs repair. For example, you may have a damaged piston pin or connecting rod. Banging can also mean you need a compressor replacement. You should stop using the unit until it is repaired or replaced.
A grinding sound from your AC usually indicates an issue with vital AC parts.
Damaged blower fan bearing or blade
Damaged AC compressor valve
Damaged condenser fan bearings
Depending on the part, you could pay anywhere from $200 to $700 to replace AC blowers and fans.
As your AC cools, it pulls moisture from the air and into the drip pan. A dripping sound suggests the condensation—or moisture—isn’t draining properly. Check the drain tube in the drip pan for blockages preventing the water from flowing out of the unit. If it’s dirty, use compressed air or vinegar to remove the clog and get water flowing again.
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. Blockages and improper installation block airflow, which produces a whistling noise. Call a top-rated ductwork contractor to inspect your ducts for blockages and the proper configuration. If they need a good cleaning, budget $370 to $490 for the cost to clean your air ducts.
When refrigerant leaks in your air handler, it can produce a hissing sound. You should address refrigerant leaks immediately, as refrigerant is harmful to the environment. Your HVAC pro mustn’t just refill the refrigerant but also find the source of the leak and repair it. R-22 refrigerant costs $20 to $50 per pound.
How to Prevent a Noisy HVAC System
Regular maintenance will help prevent many of the most common HVAC noises. But if you want to soundproof your unit even further, consider installing vibration panels or liners along your ductwork. Strategically-placed plants, shrubbery, and fencing can also act as a noise barrier, but be sure to leave enough space for your HVAC to circulate air.
Consult a reputable HVAC pro in your area to see what other soundproofing methods they might recommend for your home.