Furnace is very loud at the return grille; whistling or roaring sound.

Safety: Ensure panels are secure before operating.

• Filter type: Replace high-MERV or thick media filters with a manufacturer-approved type that allows proper airflow.
• Open returns: Make sure return grilles are not blocked by furniture or drapes.
• Door position: Try operating with interior doors open to improve return paths.
• Professional duct evaluation: If noise persists, a contractor should evaluate return duct sizing and design.