Factory or aftermarket system? Has it always sounded like that or just after you blasted some super low frequencies? “Crackley” often means blown speaker, but amp could be clipping. Gain could be set too high.
In addition to what @WarthogJr asked… make sure it’s coming from the subwoofer itself.
Sometimes when the subwoofer plays certain frequencies the rear passenger seatbelt hardware will rattle. Causes people to think their sub has gone bad when it’s actually something totally different.
More than one person has opened that up to find either the mounting bolts for the sub enclosure have come loose, or the metal on the fender where they bolt in has actually cracked.
Check all the obvious stuff first before you go tearing in there - not good odds on what I mention and what Ragnar says is much more likely