20psi boost is that to high?

[Rumcajs]

While turbo can certainly make a noise, chances are that if you can hear it that loud you have a problem. I wouldn't be surprised that either because the exhaust manifold was off/ fixed the installation got f-ed up so there are loose exhaust bolts somewhere on the dump flange/pipe/gaskets missing/blown off perhaps or even worse manifold bolts loose or gasket blown. Wouldn't be discounting a boost leak either.
Am I understanding you correctly, is this noise happening now after the recent repairs or only since the tuner bumped the boost up?
I have straight through 3" exhaust and still can't hear my turbo whistling at 18 psi. If everything is fitted and sealed properly you will only hear a faint spool up noise at best. So if it is a loud high pitch noise under load than you have either exhaust leak or possibly boost leak from loose hose, hole in the inter-cooler or else. If you didn't hear it before and now you can than .......you be the judge.