@Fernando_Pereira I was reading USB output electrical noise on Rpi 4
As I mentioned earlier in my post (as OP) that I am getting a RPi 4 to setup 7" touch screen network streamer (side by side with my CXN V2) , I hope the USB output of RPi 4 is cleaner than Intel NUC (as my previous hissing issue). worse case, I will have my iFi iPurifier 3 installed at the external DAC (D90) USB input fed from RPi4. So I need not and not intend to buy HAT on the RPi4.
What do you think Fernando? Thanks