When i turn my stereo on the ""loud" feature it makes my subs better but it can only go so high until they sound like theyre rattling??? When the head unit is "loud off" i can turn it till about volume:20 until they start to rattle again are they blown? I have only had the subs for 6 months and bought them new?

Well to start, you probably don't have your subs tuned correctly. Ideally you don't wanna be controlling subs with your headunit. Wattage should determine how loud your subs are, not signal. So let's start there.

Easy way to tune your subs = turn your subs off or all the way down. Turn your radio up until it sounds like crap (distortion). Turn it down a few notches. Turn your sub up until it sounds like crap (distortion). Turn it down a few notches. This is how loud you can run your sub, safely, with a fairly clean signal.

As far as rattling, that's never a good sign. Pull your subs and check wires and tinsel leads. If you have a multimeter, turn it to the resistance function and check the coils. If you have four ohm coils, it should read around four ohms. Same for two ohm coils, around two ohms.

How long you've had the subs really doesn't make much of a difference. You can run subs on a bad signal and blow them in a day, or do permanent damage. I'd only had my sunfire six months, but I ran it low on oil for two weeks and blew the headgasket

Hope this helps ya.

Loudness adds extra voltage and can cause clipping. If you're not running a 4 channel, put the loudness on and tune the amp with it on.

that and your most likely clipping

Rattle
Reason 1: Over excursion: The sub is being pushed out to its maximum and/or pulled in to its maximum.
Reason 2: Loose suspension (spider). The coil isn't being held in place anymore.
Reason 3: Box failure: A panel in the box could be rattling.
Reason 4: Bad CD burn: Sounds strange but I've seen it, even with storebought CDs.