Diagnosis
Dust and debris get lodged in the fabric weave. Do not use liquids or vacuum cleaners directly, as they can push dirt into the drivers or stain the material.
How to Fix It
Use a soft, dry microfiber cloth and gently wipe in one direction. For deeper dust, use a soft-bristled brush (like a clean makeup or paint brush) to lightly sweep the surface, brushing downwards.
If That Didn't Work
For sticky spots, lightly dampen a corner of the microfiber cloth with water—just enough to be cool to the touch, not dripping. Gently dab (don't rub) the spot, then immediately follow with a dry part of the cloth to absorb moisture.
Heads Up
The grille is not designed to be removed by the user. Attempting to pry it off can break the plastic clips and detach the fabric from its frame, requiring professional repair.