Surge Suppressors
MOV's (metal oxide varistors) can be used to protect circuits from transient voltages they can also reduce noice from inductive loads. The MOV contains a ceramic mass of zinc oxide grains, in a matrix of other metal sandwiched between two metal plates. A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", so MOV’s are typically used to suppress line voltage surges, and will reduce EMI from the connected device.
These also work well in DC circuits, to eliminate noise.