holy crap! i just noticed foam filter flapper doors right above my squirrel fan. i didnt know they were there! never seen them closed before. never been changed but they open and close.....what the hell? are they replaceable? do you change them from above?

 

It's not a filter.

 

isn't that the fresh air door/flap? i believe it has foam over it to deaden the sound it makes when it opens and hits something.