sounds like your power is fine
but i get thsi sometimes with my home audio setup
i think its your speaker wires or rca cables
get thick shielded cables if you can... also run your cables as far away from other cables / electronic equipment as possible.
however like mensined it could just be your amp... see if you can try another amp
if another amp makes clear sound... it gotta be cabling..
you can always take your headunit back and say its humming and they will replace it wiht another.
usually no questionsed asked for a swap