Guitar string always sounds nasty?

ok i need help, i ran out of ideas..... my 3rd string (G (in standard)) always sounds out of tune....i've have checked the intonation on all the strings...bught new strings so the gauges of the strings is correct...but even with new strings and in tune and intonation is in check the 3rd string always sounds out of tune when i try to use octaves, power chords etc...so what the crap is wrong with my guitar on that string.....its an Ibanez RG270 made in Korea (floyd rose trem system with locking nut and all that good junk)....plus i dont know if this could be the problem but worth mentioning......my pickups are rusted (natural wear and tear) maybe the pole on the pickup is messed up....but i dont thinks so becuase its the same issue when i use the other pickups.....2 humbuckers (bridge and neck) single coil in middle