Any leak in intercooler or inlet manifold when on boost will actually leak air out not suck air in.. ie. when above atmospheric temp it is under pressure and like a tyre with a thorn in it the air comes out..
this will actually cause it to run rich as metered air is not entering the engine but the ecu is injecting fuel for it.. this can cause higher knock readings as excessive fuel can cause det and also cause bogging / misfire / hessitation which will increase engine noise (which shouldn't be mixed up with knock), also cause the boost to be lower as turbo is producing same boost but some is leaking out the hole.
high pitched noise could be air leaking from pipes or dumpvalve (check jubliee clips are tight on the pipe and not just tight / at their tightest limit).
Uppipe gaskets can buzz making a high pitched noise.. they usually suck in air as the exhaust gas passes causing the gasket to buzz until exhaust gas speed is higher and you then hear the exhaust louder (sometimes noise not obvious to hear).
You are unlikely to hear an induction leak as your filter will drown out the noise.. the boost would be uneffected by running leaner with a leak in the inlet pipe, therefore I would say it is not the issue.
I would say most likely dumpvalve or jubilee clip leak or whistle is actually the turbo blades and the turbo is damaged.
Simon
|