Why is my AC making a weird noise when it turns on?
New homeowners and renters often hear unexpected rattling, buzzing, or low-level noises as soon as their heating or cooling system kicks on. These unfamiliar sounds make it difficult to identify the failing mechanical component, leaving residents unsure if the issue requires a simple DIY fix or an expensive professional repair.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Locate the mechanical space to listen for the sourceDid this help you?
- 2Search the brand and model online with blower fan to estimate parts costDid this help you?
- 3Double the parts cost to estimate technician replacement feesDid this help you?
- 4Trying to inspect the system access panel at night and using AI tools to identify the mechanical causeDid this help you?
- 5trying to catch the unit in the actDid this help you?
- 6cleaning the drain multiple times a monthDid this help you?
- 7calling HVAC technicians repeatedlyDid this help you?
- 8researching online videosDid this help you?
- 9inspecting the capacitor for physical bulgingDid this help you?
- 10checking if the capacitor sits flat on a surfaceDid this help you?
- 11Turning off the HVAC system to prevent further damageDid this help you?
- 12Waiting for the original installer to come look at itDid this help you?
- 13inspecting the fan wheel with a camera light and cleaning dust with a paintbrushDid this help you?
- 14Checking for displacement by pulling the fan out with power off and pulling the shaftDid this help you?
- 15shutting the AC off for the seasonDid this help you?
- 16pressing hard against the vent to check for vibrationsDid this help you?
- 17getting a professional to look at it in personDid this help you?
- 18Replacing the ECM moduleDid this help you?
- 19Replacing both the motor and the moduleDid this help you?
- 20Checking the bearings, play, and ohm windingsDid this help you?
- 21Checking the capacitor and contactorDid this help you?
- 22Replacing the dual run capacitorDid this help you?
- 23Turning off the system and calling a local technicianDid this help you?
- 24spraying down the sides of the outdoor unit with a hose to clean dirt and coilsDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I've had to call the HVAC company out so many times since this was installed. It's been a nightmare.”source ↗
“Every time I call someone out they say everything looks great and leave.”source ↗
“It doesn’t always make this sound, it only does this for a few minutes then runs normal.”source ↗
“Just started noticing it the last few weeks.”source ↗
“We're in a rented apartment and during the winter months (basically once the heating is turned on) we get crazy noises in the night and a constant low-level noise during the daytime.”source ↗
“Could anyone identify what is most likely to be the thing in this image that would make weird noises as described above?”source ↗
“A couple of nights ago we heard banging in our attic, it sounded like shoes tumbling in a dryer so we assumed someone was drying shoes.”source ↗
“Our bedroom was definitely not comfortable on Friday morning, and my husband called the installer.”source ↗
“We tried to turn it on last night, the sounds started, no air was coming out so we shut it down.”source ↗
“Hello everyone. I am just anxious if this sound is normal or not. This is in my daughter’s bedroom.”source ↗
“it happens when our ac turns on, we just bought the house”source ↗
“It's been pretty hot down here so it struggles a little in the heat of the day”source ↗
“HVAC unit has been making this noise a few times while running in the last few days.”source ↗
“Any advice where to go from here? Could the capacitor be going bad even if it hasn’t changed shape yet? Or is it likely something else?”source ↗
“Can I just leave it as it is? Or will it cause bigger problem if I don’t do anything about it?”source ↗
“For the past few days my unit has been making this awful noise. The unit is still working as usual for now and it’s about 15 years old.”source ↗
“Why is my AC making this noise?”source ↗
“now I get this motor sound ever since that replacement (about 2 weeks ago). Today is the worst it’s ever sounded.”source ↗
“My AC vents in certain rooms of the house make this annoying creaking noise constantly and I have no idea what it is.”source ↗
“Wife noticed this yesterday, but we're not sure how long it's been doing it.”source ↗
“FYI, I changed the capacitor about two months ago, as the original one went bad, and now that I think about it, it was also making the same noise.”source ↗
“Is your fan spinning? Sounds like a bad motor or capacitor went bad.”source ↗
“The fan is spinning. I had sprayed down the sides other sides of the unit but definitely noticed the back side was dirty. To clean it should I just hose it down with a nozzle or take the outer grills off.”source ↗
“that's what I think too but it's happening so intermittently that Im having a hard time making it happen while a tech is here”source ↗
Where this came up
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