Unit emits a persistent rattling noise only when the heater cycles on.

Safety first: Unplug and cool the unit before opening.

• Reproduce noise: Note that the noise occurs when the heater turns on and off.
• Inspect heater mounts: Open the housing and check the screws and brackets holding the heating element and shields. Tighten any loose hardware.
• Add anti-rattle pads: Where metal panels contact, you can add small high-temperature silicone pads or washers to reduce vibration (ensure they are rated for high heat).
• Replace warped parts: If a shield or bracket is warped and cannot be secured, replace the affected component or the heater assembly.