Loud noises from your HVAC system
Heating and cooling systems hum and click. New, loud noises usually point to a specific part.
What the sound usually means
- Bang or boom when the furnace starts: delayed ignition from dirty burners. Have it checked soon, it strains the heat exchanger.
- Squeal or screech: a worn blower motor bearing or belt.
- Grinding or scraping: motor bearings failing or a fan blade hitting something. Turn the system off.
- Buzzing at the outdoor unit: often an electrical part such as a contactor or capacitor.
- Rattling: loose panels or screws, or debris in the outdoor fan.
- Whoosh and hiss from a heat pump in winter: usually the normal defrost cycle.
What to do
Note when the noise happens: at startup, while running or at shutdown, and whether it's inside or outside. That helps a technician find it fast. Turn the system off for grinding, burning smells or anything that sounds like metal on metal.