Cleaning the metal rack inside a microwave works best with a soft washcloth, cotton swab or toothbrush. The best soap is mild, such as the soap one uses to wash dishes by hand. Rinsing with water and using a lint-free cloth to dry the rack and supports yield best results.
The microwave rack and supports require frequent cleaning, as any debris buildup can lead to arcing inside the oven, ultimately causing significant damage. Removing the rack for cleaning works in some models, but rather than remove the rack supports from the holes in the walls, applying a damp, soapy washcloth or a toothbrush or cotton swab that has been dipped in soapy water is the best option. Abrasive cleaners, gritty washcloths, steel wool pads and scouring pads that come with soap inside them do not work, nor do some recycled paper products.
While most microwave ovens and metals do not mix, microwave ovens with a metal rack have had their interiors "tuned" to the metal in the rack. This means that the microwaves do not have an unpleasant electric reaction when the oven turns on. When using both levels at once, cooking time is longer, but more food is heated at the same time.