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HVAC and Heating Sounds

Furnace, AC, heat pump, boiler, and ductwork noises. 41 diagnostic guides sorted by severity.

9 urgent 21 moderate 11 harmless
Urgent — Act Now
Furnace: Clicking (Not Starting)
#1 cause: Cracked or Failing Hot Surface Igniter
Act Now›
AC Unit: Hissing
#1 cause: Refrigerant Leak
Act Now›
AC Compressor: Buzzing (Not Starting)
#1 cause: Failed Capacitor
Act Now›
Heat Pump: Grinding
#1 cause: Failed Compressor Bearings
Act Now›
AC Unit: Screaming (High Pitch)
#1 cause: Compressor Internal Pressure Buildup
Act Now›
Water Heater: Hissing
#1 cause: Condensation on Hot Surfaces
Act Now›
AC Unit: Buzzing and Blowing Warm
Act Now›
Furnace: Short Cycling and Clicking
Act Now›
Furnace: Booming on Startup
Act Now›
Moderate — Investigate Soon
Furnace: Banging
#1 cause: Delayed Ignition (Gas Buildup in Combustion Chamber)
Investigate Soon›
Furnace: Squealing
#1 cause: Worn Blower Belt (Older Belt-Drive Furnaces)
Investigate Soon›
AC Unit: Buzzing
#1 cause: Failing Contactor Relay
Investigate Soon›
AC Unit: Rattling
#1 cause: Loose Fan Blade or Motor Mount
Investigate Soon›
AC Unit: Squealing
#1 cause: Worn Fan Motor Bearings
Investigate Soon›
Water Heater: Popping
#1 cause: Sediment Buildup on Heating Elements
Investigate Soon›
Water Heater: Rumbling
#1 cause: Heavy Sediment Buildup
Investigate Soon›
Boiler: Banging
#1 cause: Kettling (Scale Buildup in Heat Exchanger)
Investigate Soon›
Boiler: Kettling (Whistling)
#1 cause: Limescale Buildup in Heat Exchanger
Investigate Soon›
Radiator: Banging
#1 cause: Trapped Air in the Radiator
Investigate Soon›
AC Unit: Clicking
#1 cause: Relay or Contactor Engaging (Normal)
Investigate Soon›
Furnace: Rumbling
#1 cause: Dirty Burners
Investigate Soon›
Heat Pump: Buzzing
#1 cause: Normal Compressor and Electrical Hum
Investigate Soon›
Mini Split: Buzzing
Investigate Soon›
Window AC Unit: Rattling
Investigate Soon›
Window AC Unit: Buzzing
Investigate Soon›
Furnace: Clicking Repeatedly
Investigate Soon›
Tankless Water Heater: Noise During Use
Investigate Soon›
Ductwork: Banging
Investigate Soon›
Furnace: High Pitched Noise
Investigate Soon›
Central AC: Loud Noise
Investigate Soon›
Low Priority — Usually Harmless
Furnace: Whistling
#1 cause: Clogged Air Filter Restricting Airflow
Usually Harmless›
Furnace: Humming
#1 cause: Normal Transformer Operation
Usually Harmless›
Heat Pump: Humming
#1 cause: Normal Compressor Operation
Usually Harmless›
Ductwork: Popping
#1 cause: Thermal Expansion of Sheet Metal
Usually Harmless›
Mini Split: Clicking
#1 cause: Normal Expansion/Contraction of Indoor Unit
Usually Harmless›
Thermostat: Clicking
#1 cause: Normal Relay Operation
Usually Harmless›
Heat Pump: Whooshing
Usually Harmless›
Baseboard Heater: Clicking
Usually Harmless›
Portable AC: Rattling
Usually Harmless›
Heat Pump: Clicking
Usually Harmless›
Mini Split: Gurgling
Usually Harmless›