hi ive fitted a JBL GTO 4-Channel Amp + 12" Sub + 6x9 speakers in my car, as soon as the volume gets higher there is slight distortion like a clap, first it was on the speakers now it is on the sub - i think this system is meant to be quite powerfull so i cant understand why its doing this. also the head unit cuts out if i play the system too loud - im really confused, i think now the speakers have also developed a slight crackling noise. please can someone help