Diagnosis
Dust accumulation on the interior plastic blower wheel and intake vents is restricting airflow and can cause motor strain.
How to Fix It
Unplug the fan. Use a vacuum cleaner with a brush attachment on all exterior grilles. For interior cleaning, locate the two plastic tabs on the rear grille near the top. Press tabs inward and pull the entire rear grille cover off. Use compressed air or a soft brush to clean the blower wheel fins and interior channels. Do not immerse any part in water. Wipe plastic with a damp cloth.
If That Didn't Work
If dust is impacted on the blower wheel, you may need to partially disassemble the unit to remove the wheel. This involves removing the base, then the front grille, to access the wheel mounting clip.
Heads Up
The rear grille is not meant for frequent removal. The plastic tabs can fatigue and break. Align it carefully when snapping back into place.