LPF HPF in HU?

[typo]

Hello all, not only am i new to the DIY forums but i'm also new to DIY.
Although i've installed all my own stuff and used elementary physics to avoid melting my power supplies and some small tweaks i still know next to nothing. Everytime i have a question i always come here first to poke around.

anyways, i have a sony cdx-ca860x with HPF and LPF options in the menu. I was wondering, what do these effect? Preouts? speakers? there are 2 preouts for front and back and one for sub. I would assume the LPF is for the sub and the HPF is either for the speaker preouts or the speakers?

I have the front preout going to my CDX-GT310
and the subpreout for that going to an infinity amp for mids.

A second question i have is about deadening, which i used to dismiss untill i realized i have 11 speakers and 2 dedicated tweeters, 4 subs and a TON of rattling/resonating that just shoots it all in the foot. I paid 120$ for everything from people i knew so i'm looking for a cheap shortcut. i noticed some carpeting in my brothers basement and figured the plastic to make it water resistant would help block the airflow, while the fiber would provide insulation. i guess my question is:
how effective would this be?
i assume i should put it on the metal in between the panel with the plastic part facing the door and the fiber facing the cabin, would that be correct?

Thanks for reading sorry for the length!