This is a known effect of the Steiner Parker filter - it leaks a little audio. To hear it I have to turn everything so high up that a normal note blows out my eardrums and the walls of my studio. But yeah, it's there...
To get rid of it, simply turn down the mixer levels for any oscillators that are assigned to it, or do not assign those oscillators to the Steiner. If the Steiner is not in use at all, turning down its output also works.
The little hiss your hear, pretty low too IMO, is normal and can be managed with filter output levels and/or cutoff frequency as you have done.