A “cracker” or crackling sound from a microwave usually means arcing or sparking inside the oven, often caused by metal, food splatter, a damaged waveguide cover, or running the microwave empty.

What it can mean

  • Normal popping: some foods naturally pop or sizzle while heating, especially fatty foods or potatoes with skin.
  • Crackling or sparking: this is more concerning and often points to metal, damaged interior parts, or debris/moisture causing electrical arcing.
  • Grinding or loud mechanical noise: may be a turntable, fan, or magnetron issue rather than arcing.

Common causes

  1. Metal in the microwave, including foil or metal-trimmed containers.
  1. Food spills or crumbs inside the cavity.
  1. Damaged or dirty mica/waveguide cover, which can arc and crackle.
  1. Empty operation, which can cause popping and damage.
  1. Internal component problems if the sound is electrical and persistent.

What to do

  • Stop using the microwave if you see sparks or smell burning.
  • Unplug it and inspect for food residue, metal items, or a burnt waveguide cover.
  • Clean the interior and remove any metal objects or damaged accessories.
  • If the noise continues after cleaning, or heating is weak, get it serviced.

Safety note

If the crackling is accompanied by visible sparks, burning smell, or repeated arcing in the same spot, treat it as a safety issue rather than a harmless noise.

TL;DR

Crackling sound in a microwave usually means arcing , not a normal operating sound, and the safest first step is to stop using it and check for metal, spills, or a damaged waveguide cover.