Loud rattling or vibrating noise during operation, especially when compressor starts.

Safety: Unplug the unit before tightening or adjusting parts.

• Check installation: Ensure the unit is firmly supported and not rocking. For window units, verify the mounting kit is tight and foam seals are properly installed.
• Tighten screws: Remove covers and tighten all accessible screws on panels, fan housings, and brackets.
• Inspect fan/blower: Look for bent fan blades or debris stuck in the blower. Straighten minor bends carefully and remove debris.
• Compressor mounts: Check that the compressor mounting bolts and rubber grommets are intact. Replace worn compressor mounting grommets if the compressor is banging against the frame.
• Panel padding: Add thin foam tape between vibrating metal panels if needed to reduce noise.