See if all the screws around the edge are tight. Also you can cram some poster putty in spots that you think are causing the rattling noise. It could be the latch.
If it is the same as their slightly smaller cases based on the Antec SX-6xx Performance Series, the handle can be removed in you think that could be causing the problem. Also if you do not open the case too often, you can add 3 screws to secure the door.
I think they also use little metal tabs to make sure the seal on the door is tight. These tabs might not be making enough contact.
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