The subwoofer in your home theater system serves an important purpose. It reproduces the low frequency musical notes and sound effects of a movie's soundtrack, ensuring full, rich sound and real impact when watching a movie. A rattle can be annoying and take away from the enjoyment of your listening experience. In many cases, you can remove the rattle with a bit of common-sense and a few simple solutions.
Reposition the subwoofer slightly. If the subwoofer is too close to objects in a bookcase or on a shelf, it may cause them to move, creating the rattle. Try positioning the subwoofer in a different location if this is the case.
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Remove any objects from the top of the subwoofer enclosure. It may seem obvious, but if you've placed something onto the subwoofer it could be causing the rattling sound.
Turn the subwoofer onto its side and examine the feet on the bottom, if it has them. Tighten the screws holding the feet onto the enclosure.
Check the cabling connections to the subwoofer. Make sure that none of them have slipped part-way out and are rattling against the jack.
Pull the grille cover off of the subwoofer and tighten the screws on the perimeter of the subwoofer. If the screws are loose, the subwoofer may be rattling against the sub opening in the enclosure.