I was using the LFE sweep during the front/left subwoofer test and noticed that something was rattling near my sub. I put my ear down and it sounds like it is coming from inside the sub. It isn't nearly as noticable when trying the center/sub LFE test. Is my sub blown? Do other people have this noise? The reason for my concern is that it is a new REL Storm III. I haven't noticed anything bad during normal listening, but I haven't been listening to it alot recently. I have a decent Yamaha amp with JMlabs Cobalt bookshelves and center.