My bike does the same thing and I have taken them off cleaned the rotors and brake pads but it is still there. I don't know what else to do but get new pads but the ones I have on now have plenty of miles left on them???
go out find a long straight road with no one on it and do a good 8 or so 60 to 5mph stops... HARD stops... almost nose wheelie stops.... BUT NEVER FULLY STOP... then ride for a couple of miles without touching the breaks to let em cool down... id bet they dont squeak after that.