hi, i got an alpine headunit, i got my 2 subs and 2 6x9s running off my amps in my boot, they are running fine with no interference. When i crank my volume up, all my 4 standard car speakers in my doors and back seats, kinda crackle. they aint distorting because i know the sound when they are distorting. its wierd that its doing it too all 4, and its only started doing it today! there is no interference with the speakers, but my mate was fiddleing with my headunit, but it wasnt turned on! every since he fiddleed with it, the speakers have made that noise.
check the high pass filter setting for the door speakers on the Alpine head unit. they should be set to 80 or 125Hz he may have turned the filters off or down so they're bottoming out now