If you are trying to find a hidden rattle in your guitar, investigate the possibility of a loose truss rod in the guitar neck. Sometimes this rod can be too loose or it can be touching the truss rod channel just enough to cause a slight rattle with the strings vibrate.

Wood Jacks To Repair Loose Braces Source: Crack and Brace Repair Repair Loose Braces With Wooden Jacks: Tools and materials Required: Assorted Wood Jack Sticks: 20 gage Hypodermic Needle: Titebond III Glue Mechanics Inspection Mirror LED Work Light Wooden Cam Clamps: You have found a loose brace or loose braces and have clearly marked their [...]

Crack & Brace Repair Source: Screw Jack Brace Repair Method Repair a Loose Braces With Screw Jacks: Tools and materials Required: 3″ Screw Jacks: 20 gage Hypodermic Needle: Titebond III Glue Mechanics Inspection Mirror LED Work Light Wooden Cam Clamps: You have found a loose brace or loose braces and have clearly marked their locations. [...]