DIAGNOSIS: A foreign object is likely lodged in the fan blades, or the filter is not seated correctly and is vibrating against the housing. A loose internal component is also possible.
FIX: Power off and unplug the unit. Remove the filter assembly. Inspect the fan blades through the opening for any debris (hair, paper, toy parts). Use a flashlight and tweezers to remove any obstruction. Reinstall the filter, ensuring it clicks fully into place and the cover is securely closed.
IF THAT DIDN'T WORK: Check that the purifier is on a perfectly level, hard surface. On carpet or an uneven floor, the housing can vibrate and resonate. Move it to a level hardwood or tile floor. If the noise persists, the fan motor bearings may be failing.
HEADS UP: Do not operate the purifier with a persistent rattling noise. A foreign object can unbalance the fan, causing excessive wear on the motor shaft and bearings, leading to premature failure.