Air conditioners make a steady hum and the whoosh of air. New or louder sounds are worth paying attention to, because they often show up before a breakdown.
Buzzing
A loud buzz from the outdoor unit often means an electrical problem: a failing capacitor, a worn contactor or a motor struggling to start. If the fan isn’t turning, shut the AC off.
Banging or clanking
Something loose or broken: a fan blade, a motor mount, or a part inside the compressor. Turn the system off and call; running it can make the damage worse.
Squealing or screeching
Usually a motor bearing in the outdoor fan or indoor blower, or a belt on older blowers. High-pitched screeching from the compressor is more serious.
Hissing or bubbling
Can indicate a refrigerant leak, especially with weak cooling or ice on the lines.
Clicking
A click at start and stop is normal. Constant clicking can mean a failing relay, thermostat or control.
Rattling
Loose panels, debris in the outdoor unit or a loose duct. Check for sticks and leaves first.
Gurgling or dripping inside
A clogged condensate drain. Left alone, it can overflow and stain ceilings or shut the system off.
For anything beyond debris and loose panels, call (312) 924-7223 for AC repair in Chicago. For ductless systems, see mini split repair.