If your subwoofer is making rattling noises at all or some frequencies, it is likely that the surround (rubber or foam ring that connects your woofer cone to the basket) has deteriorated or the glue has come loose.  You can check this by removing the grill and inspecting the surround visually.  If a problem is found, you can contact our support team about your specific subwoofer – some subwoofers can have their woofers replaced while others may need to be rebuilt.