This problem has always plagued me in some form or fashion, but at least with Cubase 9 it was manageable. This is a common problem I realize, yet the common answers do not seem to resolve this issue.
-Cubase Pro 9.5
-RME Fireface UFX USB
-RME TotalMix FX Mixer > Main Out -10dBV, Individual channels set at +4dBu
-Clean Cubase Template, no plugins
a) Empty template automatically seems to be picking up noise from some source, no microphones are near and/or even connected.
b) Noise is a hiss-like static as you’d might expect from changing an individual channel from +4dBu to -10dBV.
c) The soundcard that came with the computer and the drivers have been disabled.
d) No noise when Cubase is closed or TotalMix is set to Full Mode as opposed to DAW Mode.
With version 9.0 I had this issue, but it was to a much lesser extent. Now the hiss is more intrusive and comes in and out for relatively long periods of time.