DIAGNOSIS A sudden rattling or buzzing is almost always a foreign object (like a toy, paper, or large debris) lodged against the fan blades inside the base.
FIX Unplug the unit. Tip it upside down and gently shake it over a trash can. Look through the bottom intake grille with a flashlight to see if anything is stuck. Use long tweezers to carefully remove any obstruction.
IF THAT DIDN'T WORK The noise could be a loose internal component from a drop or impact. This requires contacting Levoit support for a warranty assessment—don't try to open the motor housing yourself.
HEADS UP Never run it with a persistent rattling noise; it can damage the fan motor and void your warranty.