My rear left speaker rattles only when there's bass in a song. If there's little/no bass it doesn't rattle. To stop the annoying rattle i have to turn the bass all the way off and it sucks. Is there anyway I can get the bass off that ONE speaker?

 

I'd recommend replacing it. You can get stock speakers for a stick of gum, and some loose change. Otherwise check out bassblockers at Crutchfield.com.