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

Safety: Unplug the unit before tightening or adjusting any parts. Beware of sharp metal edges.

Steps:

• 1. Check installation: Ensure the unit is firmly secured in the window or wall sleeve with all brackets and screws installed. Add foam strips where the cabinet contacts the frame to reduce vibration.
• 2. Tighten screws: Remove the front grille and tighten any loose screws on the blower housing, control panel, and chassis.
• 3. Inspect fan blades: Look for bent or cracked indoor blower wheel or outdoor fan blade. Replace if damaged. Ensure they are centered and not rubbing against shrouds.
• 4. Compressor mounts: If the noise is a heavy thumping when the compressor starts, the rubber mounting grommets may be worn. Replacing them is possible but often requires significant disassembly; consider a technician.