Fordman2011

i have the mach 460 sound system but have an aftermarket alpine head unit, it was this way when i got the car. there are no amps in the trunk and when i turn on any bass it makes a terrible scratchy noise, same with treble. without either turned on it sounds ok as long as the volume isnt too high. it may have had an aftermarket system but im not sure. if not is all i need amps and how do i tell if my speakers are blown? how do i tell if it had an aftermarket system?