[rotrex]

Yes, I have only used pre-turbo injection during this test.
I injected about 300ml/min.
I have no spool time as I use a mechanically driven supercharger, a Rotrex C30-74 at the time. It spins to 120000 rpm. The compressor wheel plus housing itself is actually from Garret.

The noise is a white noise sound. It sounds like a small boost leak or a compressed air blow gun being opened in your engine bay.
No scratching or whinning. It is a flow related noise. It is more a altered turbine sound rather than a additional noise. It completely changes the thermodynamics of the compressor, so that may as well induce a different sound.
My car has no sound insulation besides one piece of carpet on the fire wall . You cannot hear the radio past 30mph. But your hear everything that happens in the engine bay. The engine sits right behind the seats.