DIAGNOSIS The noise is typically caused by the compressor or fan assembly vibrating against the cabinet or a loose internal component.
FIX First, ensure the unit is on a solid, level floor—not on carpet or a wobbly surface. If it is, unplug it and check that the side and rear grilles are clean and unobstructed. A high-pitched buzz often means the fan blade is hitting a buildup of ice on the coils, which points to a room temperature issue (see below).
IF THAT DIDN'T WORK A persistent metallic rattle could be a loose screw on the internal fan shroud or a compressor mount. This requires removing the outer cabinet, which may void your warranty if you’re not comfortable.
HEADS UP These units are designed to run in temps above 65°F. Using it in a colder space (like a basement in winter) will cause the coils to frost over rapidly, making the compressor work harder and creating a different, cyclical buzzing noise.