Crackling/popping sound coming from my car speakers?

1st..the head unit is either 4-6 watts rms or 18-24 watts rms...the other problem is your new or old speakers had a higher rating than that ssay 45-100 watts...factory or aftermarket radios are only true sound up to 40 percent of the available volume which means if your radio has a knob on it ...from where it turns on usually around 7 o'clock range clear volume music is only good to 11 o'clock. if it has a on up/dn the high side is say 60, then good volume is at 25....anything after that is 10-20 percent distortion and that is not good for the speakers