What is causing this sound and some other questions...

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Hello,
Can anyone tell me what is causing this sound?
YouTube

Is this spider hitting the bottom?
The reason I am asking is because I would like to change the magnet and coil to bigger (I would go from 30w to 100w -just for fun), but I don`t know what is causing this sound when I overpower the woofer.

I would also like to know if I can get T/S info (to build L port box) by measuring the original ported box.

Thank you for help
 
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