why does my sub pop at high vol

if the subs make a poping noise when your cranking your system it usually means the voice coil is moving to much in the magnet and it's bottoming out....or in simple terms, your trying to make the cone of the sub go further then you it's able to...it's like reving a honda up to 9000 rpm and expect it to run after    but as to why it never did that befor untill just a little while ago..the subs could be getting weakerand almost at the end of there life...as short as it was..or will be...

also another peice of info...if the sub says it'll handle 400 RMS then depending on the box design (ported, sealed,etc) will also affect how much power a sub can handle befor it "bottoms out" a ported box doesn't need as much power to push the sub as hard as in a sealed box,

there's just one thing questioning me...you said you have 3  sub and running at 2 ohm...did you series 2 then parallel them down to 2 ohm? or did the store you went to hook them up and tell you there at 2 ohm...because 3 - 4ohm subs parralled is 1.33 ohms...which would change your output numbers and make them higher.

This is very unwise.  Your amp is most likely clipping like a weed wacker on steroids.  Probably sounds about as good, too.  Turn that sh*t down and set it up properly, unless you don't care about blowing yur subs rather quickly.

Nope.  Setting the gain properly is the only thing you can do to avoid frying your speakers, no matter what they are.

That's a very funny analogy there DYohn, LOL!

Ok try  http://www.bcae1.com and read it a few times maybe. Select number 63 on the right.

After that, maybe some further explaining could be done.