Fix / Split System AC — Outdoor Unit / Making noise

AC (outdoor) making noise?

Worn internal compressor components or refrigerant slugging produce loud knocking or rattling sounds during operation.

• Hermetic Compressor

  Call a Pro Part: $250–$600

• Propeller Fan

  Moderate DIY Part: $30–$80

  A bent blade or debris contact causes the propeller fan to vibrate and produce a rhythmic thumping or whirring noise.

• Accumulator

  Call a Pro Part: $40–$120

  A failing accumulator with internal deterioration can rattle as liquid refrigerant sloshes inside at startup.

• Four-Way Valve

  Call a Pro Part: $60–$180

  A partially stuck four-way valve can buzz or hum loudly as it struggles to shift between heating and cooling modes.

• Front Grille

  Easy DIY Part: $20–$60

  A loose or cracked front grille vibrates against the cabinet at high fan speeds, producing a rattling noise.