i just need some advice and really need some help, ok so i have a pioneer headunit that is brand new with 2x rca preouts one goes to a 250rms sub and the other goes to a 4 channel amp that powers 2 rear speakers (type s alpine rated 80 watts rms) and 2 jvc front component speakers rated at 60 watts rms the problem im having is that when i turn my HU up past 25 (goes to 62) the speakers start to bottum out and pop, this is when the 4 channel amp is on the normal setting (had LPF normal and HPF setting) when i put the amp to HPF the popping stops but why are these speakers doing this they were fairly expensive oh and by the way the 4 channel amp puts out 60 watts rms at 4 ohms (all my speakers are 4 ohms) ive checked wiring and all seems to be fine positive to positive negative to negative etc the weird thing is that i had my settings on normal and i dont remember the speakers popping i had the head unit up to 50 with no distortion (only for brief period for testing ) and then now they pop really loud and dont sound good at all when the amp is on normal setting any help would be appreciated (the 4 channel amp has been swaped to thats not the problem and so has the headunit) when i look at the speakers when on hpf setting they dont fluxuate alot but when ojn normal setting they seem to have a much larger range of movement. my grounds are fairly solid as well could it be a ground loop issue speakers partially blown??? thanks guys