Problems with RT3000p sub

dpd

My sub portion for the right RT3000p seems to make a static popping noise here and there. I had this problem about four years ago in the same speaker and bought a monster surge suppressor and it seemed to take care of the problem. Along with using a different outlet. I believe I had a ground loop issue. I would say that it has worked perfectly for the last four years and now it is starting again. I checked the woofers and they apear to be ok. My surge surpressor says that it is grounded also. I am not sure if I need a new amp or if there is another test I could try. Any help or ideas would be great.
Thank You
Don