I have a 2002 jetta 4cyl 1.8t with 90A alternator and i want to run a 750.1 kicker amp with 2 cvr 12"?

I bought a floor model amp from best buy and when i turn my subs up pretty loud my protection light on my amp either flips totally on and shuts my subs off completely or it will flicker and take some hits out and come back on instantly. I also had a weird occasion where i turned my car off and went in my house for about 30 minuets came back outside used my keys to pop the hood and the amp turned on without my car started or keys even in the ignition and the subs flexed for about 3 seconds and now its turning on and off... also one more effect im having is whenever i turn my car off my amp will not turn off and it flickers back and fourth between the protection light and the red ring around the ZX which means i have power. all the wiring and mounts and everything is fine so it is not that.. I'm thinking it is either my alternator or my amp.. my amp is the 750.1 kicker amp it has 2 40a fuses. and my alternator is 90a should my alternator be causing defects like this? or is it my amp that i need to buy and replace?