Redbone
The two prong plug will not fix the problem, that's if you have a ground loop symptoms is a continous hum from the speaker. I have the same popping sound before if there are any fans or motors that are being turn on and off.
I haven't heard it lately after I installed a power conditioner such as the Monster HTS-5100. Surge protectors will not eliminate it. I am not saying that the problem is fix, it might just be a coincidence. If you find something else that would fix it please let me know.