Reeee noise on boost

[Stevieb_08]

Just had the engine out of my 2006 impreza Sti to do the head gaskets (shock). It is now refitted to the car and I'm experiencing a reeeee sounding noise at about 0.4 Bar, getting louder up to 1.1 Bar where the boost limit is hit. 

I also have code P2021 "Intake runner position sensor/switch low bank 2 c" showing but disappears and stays off for the duration of the drive when reset, but the reeee noise was there from the moment the engine was boosted the first time, where as the code didn't appear until after the MOT last weekend. As far as I'm aware the garage didn't touch the engine. Previously it was showing the same code but on bank 2 a, but this was sorted by installing the sensor correctly as I hadnt previously.

Anyone have any ideas on what the noise could be and if its related to the code, and if there is a sensor c on the ej257 intake runners/TGVs? All hoses are tight and ftted correctly around the intercooler and turbo.