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Common AC Noises and What They Mean
Air conditioners can make some strange sounds — but not all of them mean trouble.
From banging and buzzing to clicking and hissing, every noise tells a story about what’s happening inside your system.
This guide explains the most common AC noises, what they actually mean, and when it’s time to call a professional. Calgary homeowners can save time (and avoid bigger repairs) by knowing what to listen for.
When Your AC Sounds Like a Rock Band
Air conditioners should hum along quietly in the background. They're not supposed to sound like a drummer auditioning in your living room. If yours is clanking, buzzing, or hissing, don't panic. Most noises have a logical explanation—and knowing what they mean can save you from sweaty nights and expensive mistakes.
Let's decode the greatest hits (and flops) of AC noises, Calgary edition.
The Banging / Clanking
What it sounds like:
Metal-on-metal, like a loose washer rattling around a dryer.
Likely causes:
  • Loose fan blade or motor mount inside the outdoor unit
  • A stick, rock, or ice chunk got into the fan housing
  • Worn-out compressor parts (bad news if it's that)
Safe DIY checks:
  • Turn off the breaker and peek into the outdoor fan—remove any obvious debris.
  • Tighten visible screws on the unit's access panel.
When to call a pro:
If the banging is constant or inside the sealed compressor, you're not fixing this with a screwdriver. That's pro territory.
The Hissing
What it sounds like:
Like someone letting air out of a bike tire.
Likely causes:
  • Refrigerant leak (the most common, and the most serious)
  • Air leak around duct joints or a cracked plenum
  • High-pressure valve releasing air
Safe DIY checks:
  • Stand near the indoor coil or outdoor unit—pinpoint where the hiss is coming from.
  • If it's in ducts, wrap suspect joints with foil tape (not duct tape).
When to call a pro:
Refrigerant = licensed tech only. Don't poke, prod, or try to refill a system yourself. Not only illegal in Canada, but unsafe.
The Buzzing
What it sounds like:
A swarm of bees parked in your backyard condenser.
Likely causes:
  • Electrical issue: failing capacitor, loose wiring, or a contactor starting to arc
  • Frozen coil beginning to thaw (ice buzzing and crackling)
  • Loose outdoor fan motor
Safe DIY checks:
  • Turn off power and look for visible ice on indoor coils or lines.
  • Replace the air filter if clogged—it's often the root of coil freezes.
When to call a pro:
Buzzing + breaker trips = electrical. Leave it alone. Capacitors and high-voltage wiring are a no-go for DIY.
The Clicking and Screeching
The Clicking
What it sounds like: Rapid clicks, like someone nervously tapping a pen.
Likely causes:
  • Relay switches engaging (normal when it starts/stops)
  • Continuous clicking = bad capacitor, failing control board, or stuck relay
  • Loose thermostat wiring sending ghost signals
Safe DIY checks:
  • Swap thermostat batteries.
  • Double-check wires are snug at the thermostat.
When to call a pro: If clicking repeats nonstop and the unit doesn't start, you'll need diagnosis tools (multimeter, capacitance testing).
The Screeching / Squealing
What it sounds like: Like a banshee or a car belt going.
Likely causes:
  • Worn or dry motor bearings
  • Failing blower motor or fan motor
  • Loose belt on older units (rare in modern systems)
Safe DIY checks: None. Don't spray WD-40—it won't fix motor bearings.
When to call a pro: If you catch it early, a motor bearing lube or replacement may save you. Ignore it, and you're looking at motor failure.
The Gurgling and Loud Pops
The Gurgling / Bubbling
What it sounds like: Like someone blowing bubbles through a straw.
Likely causes:
  • Refrigerant gurgling through low charge lines
  • Clogged condensate drain gurgling water back up
  • Air pockets in refrigerant line
Safe DIY checks:
  • Check and clear condensate drain with a wet/dry shop vac outside.
  • Make sure drain line slopes properly.
When to call a pro: Refrigerant bubbling is not DIY—licensed work only.
The Loud Pop / Boom
What it sounds like: A shotgun blast from your vents (hopefully not literally).
Likely causes:
  • Ductwork expanding/contracting with pressure or temperature
  • Dirty filter causing pressure buildup
  • Improperly sized ductwork or dampers snapping shut
Safe DIY checks:
  • Replace filters regularly.
  • Listen for which vent it's coming from.
When to call a pro: If it's violent or frequent, you need airflow balancing or ductwork adjustments.
Calgary-Specific AC Noise Triggers
Because our climate loves to mess with us:
Snow & Ice
Spring meltwater freezing in your outdoor unit creates cracks and bangs.
Wildfire smoke
Filters clog faster, starving airflow → buzzing, clicking, coil freeze → noise.
Temperature swings
Big daytime swings stress ductwork and cause pops/booms.
Safe DIY Checklist and When to Call a Pro
Safe DIY Checklist (Quick Reference)
  • Check and replace filters (especially during smoke)
  • Peek into outdoor fan for debris
  • Clear condensate drains with a shop vac
  • Swap thermostat batteries
  • Tighten obvious panel screws
Stop there. If it involves refrigerant, gas, or live electrical, that's pro territory.
When to Definitely Call a Pro
  • Gas smell + any noise (urgent)
  • Repeated breaker trips
  • Screeching motors or constant buzzing
  • Ice on coils + hissing/bubbling
  • Loud banging inside the compressor
Professional Solutions and Long-Term Prevention
What the Pro Will Do
  • Check refrigerant charge properly (superheat/subcool numbers)
  • Test capacitors, contactors, and wiring with meters
  • Inspect blower motors and bearings
  • Pressure-test refrigerant lines for leaks
  • Balance airflow and dampers
How to Keep the Noise Down Long-Term
  • Annual tune-ups (clean coils, check charge, lubricate motors)
  • Keep bushes/grass trimmed back 2–3 feet around condenser
  • Change filters on schedule
  • Don't oversize/undersize replacements—proper sizing reduces stress/noise
Your AC Shouldn't Sound Like a Horror Movie
A little hum? Normal. A rock concert in your ducts? Not normal. Now you know the usual suspects. Do the easy checks, call a pro when needed, and keep your Calgary home cool without the sound effects.
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