distortion...

alright i got a kicker 08ZX500.1 amp and a MA Audio 1000xl wired 2ohm.
it sounded great when i installed it and got better once i tuned the level and gain a little. but today i was jammin and the bass sounded kinda flat. the sub was still hitting hard and loud but it sounded a little off.. i played with the knobs on the amp and nothing really helped.
 
the problem might no tbe with the sub/amp though, the radio i have is a cheapo Olympus that came in the truck. i dont know if something could have gone wrong with the radio or what.. i checked the power, ground, and rem wires for the amp and they all seem fine, no pinches or loose crimps or anything.
 
could the problem come from the radios ground being bad?
 
any help would be great. thanks