Stereo interference

Hey, I'm having a little trouble with my stereo. When the engine is off (acc on), my stereo sounds great, I can crank it up and have perfect bass and all. When the engine is running though, I can't turn it up too loud b/c it crackles and stuff, I guess from engine interference. What can I do about this? I have the power lead hooked up to a post on connected to the fuse box. Is this ok? Is this what's causing the noise? Any help is appreciated. BTW, I have a JVC El Kameleon (LX30), Infinity kappa 6 1/2's, and Infinity kappa 6x9's. Thanks for the help!