can't figure out belt squeak

hi i noticed a squeak about 3 months ago on my truck so i replaced the serpentine belt.well it quit for a day or two then it started up again but worse.took it to a machanic and apperently they just spray some belt dressing on it and it stoped.but then again it started back up after a day or so of driving.i noticed after they sprayed the belt my pulleys and everything are coroded with a greasy film.so i'm assuming this was caused by the belt dressing they put on it.anyway it still squeaked worse then ever so i replaced the tensioner pulley and the idler pulley and even changed the belt again.it stoped for a day or so but yet again it started squealing bad.well after that i figured maybe my a/c compressor was going out or something so i replaced my belt with one to bypass the a/c compressor.well again it stoped and within a few hours of driving it started back up.i've listed to try to pin point where the noise was coming from and it sounds like its coming from the smog pump pulley but i'm not really sure.do you have any suggestion's on anything to look for and if i should change the smog pump pulley how do i go about keeping the pulley still while i loosing the bolts?your help is greatly greatly appreciated.thanks.........