ive got two rs turbos.
ones got a standard turbo, panel filter and 12psi,
the other has got a stage 3 turbo and 24psi.
the standard one still whistles (excuse my spelling, its shite) although it whistled more with a cone fillter on it.
the stage three sounds much much louder.
i thought it was just the air going through the compresor housing that makes the noise,