Identify where the sound starts
Stand a safe distance away and note whether the sound comes from the indoor equipment, outdoor unit, vents or another nearby source.
Describe the timing
Record whether the noise happens at startup, throughout the cycle, during shutdown or only when the fan runs.
Know which sounds require shutdown
Turn the system off for grinding, metal-on-metal sounds, severe banging, electrical buzzing with heat or odor, smoke or repeated breaker trips.
Avoid opening the equipment
Loose panels, motors, fans, electrical components and compressors require safe inspection. Do not remove covers or reach into the unit.
When to request professional service
Request service when basic settings and an accessible filter do not explain the problem, or when the system is frozen, leaking, electrically unstable, unusually noisy or unable to maintain a safe indoor temperature.
Shut the system down for smoke, a persistent burning smell, repeated breaker trips, spreading water or severe mechanical noise. Call emergency services for fire, medical danger or another immediate threat to life or property.