do you have a wireless mic system hooked up to the system? At one of my clubs I designed and installed the system at.. they got s new wireless mic to add to the system.... but they put it right next to the DMX controller. They called me up that night saying the same things... i rushed over there.. just to find out that the recever was picking up interfreanace comming from the DMX light controller (alot of DMX controllers will cause this if you put your wireless mic to close). So check to see ifyou are gettng any interfearnace on the wireless mic if you have one... if it is.. you mic have to change feq the mic is using.. or with some mic.. get a diff one on a diff freq.

nope no mic just two turn tables, mixer and headphones

ok.. then check your RCA cables... you might have a bad cable.... had this happen with a used table i got.. hooked it up and thats all i could hear was poping.. replaced the cable and worked fine.