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

Safety: Unplug the unit before tightening screws or touching internal parts.

Steps:

• Check external panels: Tighten all visible screws on the cabinet, front grille, and side panels. Add foam tape between rattling panels if needed.
• Inspect fan blades: Remove the cover and check that the indoor and outdoor fan blades or blower wheels are secure on their shafts. Tighten set screws and reposition blades if they rub.
• Compressor mounts: Verify that the compressor mounting bolts and rubber grommets are intact. Replace cracked grommets to reduce vibration.
• Level the unit: Ensure the unit is level and stable. For window units, use shims to prevent the chassis from twisting.