['Step 1 - Make Sure the Unit is Properly Installed. The annoying rattling sound you hear may simply be because the air conditioner is no longer tight in the window frame. ... ', 'Step 2- Check Front Panel Screws. ... ', 'Step 3- Examine the Fan Blades. ... ', 'Step 4- Lubricate the Fan Motor. ... ', 'Step 5- Straighten the Coil Fins.']