Serpintine Belt Noise ??

Hi there,
2006 xterra,Purchased back in may 18,000 mi., developed belt noise 2 weeks after purchase, changed to new belt and tensioner, good for another 2weeks, noise came back ?? checked pulley alignment noticed power steering pulley about an 1/8 inch out, no problem to it to work machined as required, cleaned all pulleys with brake cleaner and wire brushes, sqwealing noise back again?? starts out with chirping at start up and goes away as it warms up, as days go by it (the noise) continually gets worse untill its sqwealin all the time,change belt repeat process, any ideas, your imput would be greatly appreciated !!!
thanks Steve