are my subs blown or are they not? <<click for all information :]>>?

[EddywardStemp]

ok, sooo, i have two alpine type R 12" subs that can handle 1000W RMS, they are receiving 500W RMS a piece. when i first installed them into my car, my amp was turned up only about 75%, yesterday i decided to try turning the amp up ALL the way to see how much harder my subs would hit. so i turned them all the way up.. well my results wernt as i expected, with my back seat up, they sounded like they hit alot softer, but with my back seat down, they sounded like they were hitting alot harder(than before, with my back seat down) i didnt understand why they sounded softer with my seat up, it bothered me, so i decided to mess with my amp today. what i did was i messed with the "freq", and the "gain" dials, what i did with those is turned them till it sounded like my subs were hitting hard.. i finally got to the point where both dials were turned up all the way, after driving for a minute, i noticed my subs seemed like they were hitting way to hard, not to hard but they were making this REALLY loud rattling noise, so i turned the gain and freq dials almost all the way down. my subs still have the loud rattling noise, but they hit ALOT harder than before, with the dials turned almost all the way down. im not sure if messing with the freq and gain dials blew my subs out of know where or if my subs sound just bad because i changed the dials.

so basically, with the back seat up, while driving, my subs are hitting VERY hard, but when i open the trunk or pull the back seat down for a louder effect, i hear the really loud rattling, you can tell its coming from the inside of the sub box, and not just something rattling in the trunk. so are my subs blown or do they just sound bad cause i messed with those dials?