Diagnosis
The magnetic fabric grille traps dust and pet hair. Do not use liquids or vacuum cleaners directly on it.
How to Fix It
Gently pull the grille off from the bottom corners. It is held by magnets. Use a soft-bristled brush (like a clean paintbrush or makeup brush) to lightly brush the dust off the fabric. Brush in one direction.
If That Didn't Work
For ground-in dust, use a slightly damp, lint-free microfiber cloth. Wipe gently in one direction. Do not soak the fabric. Let it air dry completely before reattaching.
Heads Up
Never remove the internal metal mesh behind the fabric grille. That protects the speakers. Only clean the removable outer fabric cover.