Echelon04

I just replaced my stock speakers. They are running directly from the headunit which is also after market. I had the after market radio in already and it sounded fine, but when I changed out the speakers the drivers side rear speaker is buzzing, but only when I drive. It's not really a buzzing sound, but more of like if you had pop rocks in your mouth and you put your fingers in your ears. I know it's a bad ground somewhere, but I dont understand why it would surface all of a sudden? I am so pissed about this. What do I need to do to fix it? I have checked all the connections and everything seem fine. Thanks for your help.