Choppy Sound when playing mp3's

[gf4200isdabest]

Hey guys. When I play mp3's on my computer at full volume, I hear a lot of static in the back. This happens regardless of whether it's encoded at 128 or 320 Kbps!! I can play normal (commercial) cd's fine on it but making mp3 cd's won't play crisply either. I'm really at a loss for why this happens. I'm running Windows XP with an Altec Lansing 4100 speaker system and a Turtle Beach Santa Cruz sound card. Do you guys think there is something wrong or am I just playing them too loudy?

Thanks!