Okay! Took the turbo apart.......and both compressor and turbine wheels are undamaged and in good condition. There is a good amount of shaft play, which explains why I was hearing that ringing noise once in a while. Would this be the reason why I was humming at the intake side, and the boost not being responsive? How would boost leak if the bearing is bad? Would I be safe without re-balancing if I marked everything as-is prior to disassembling? Overall everthing looks simple enough to do............