I am bit disappointed about Hifiberry. First installation was very frustrating due to missing information what driver to use and what (raspi driver) not to use. It is now working with a clean installation of Raspi OS-Lite 64 bit without desktop (remote only). One important thing to hear music is to disable DRM VC4 V3D Driver (!).
I can not find any hints in the sparely installation documentation.
Okay it is running now and putting out music. But anyway I am also disappointed about the noise on the output. And there is no defect this noise is existing when nothing plays and also when something plays. I tried two different (new) Raspberry Pi 4 with 2 new Hifiberry. This problem seems to be system immanent. It is not heard as frequency is above 20 kHz but if you want signal processing this can be very disturbing. We are talking here about short pulses every 50us with an amplitude of about 1V (!).
This noise is even with no running playback (silent).
This is when it is overlayed to music.