rumble sound from subs when i turn on/off cd player and when i turn bass knob up

ill start with saying i have a sundown audio saz-2500, two DD 2512s ported bbox, optima yellow top, 0 gauge streetwire wiring kit.

ground is connected to a seatbelt bolt in back seat.

from subs to amp i using 8gauge..theres terminals on my amp so i basically have both wired seperatly at 2 ohm each...(pos to pos to pos neg to neg to neg) so if im right that equals 1ohm load

problem: when i turn the bass knob up i head a rumbling sound (only first few notches on knob though) and when i turn the cd player on (when amp turns on) you hear kind of a pop sound