Diagnosis
Dust buildup on the internal blower wheel is causing reduced airflow and noise. The grille isn’t meant to be fully removed for routine cleaning, but you can get in there.
How to Fix It
Here’s the safe way. 1) Unplug the fan. 2) Use a can of compressed air (like for electronics) and a vacuum cleaner with a brush attachment. 3) Aim the compressed air through the rear grille slots to blow dust off the blower wheel and out the front. Hold the vacuum nozzle nearby to catch the cloud. 4) Use the brush attachment on both grilles. For stubborn dust, a long, thin bottle brush or a damp cloth wrapped around a butter knife can be carefully worked through the slots.
If That Didn't Work
If the dust is caked on, you can partially disassemble it. Remove the few screws in the base, then gently work to separate the front and rear halves of the shell. This gives you direct access, but be patient with the plastic clips.
Heads Up
Never run water into the fan or submerge any part of it. Don’t try to force the grilles apart without removing the base screws first—you will break the plastic tabs.