I doubt that thousands of audio professionals and enthusiasts throughout the world would keep buying and using RME USB interfaces if there was any truth to your concern/question.

I have a Babyface Pro Fs and UCXII. They sound fantastic and work wonderfully via USB

Your USB-noise is related to USB cables or USB connectors ?

Interesting box with no other function than to allow USB to work as normal.
Can't see any relation to audio...

Some posts in this thread explain a few possible reasons for noise.
https://www.audiosciencereview.com/foru … ise.29399/

I'm not an electronics expert, if you want expert advice, I would contact one or write an e-mail to RME support.
Because you are asking in a user forum, my understanding of this is this:

I wonder about the statement, too, that Firewire should be less noisy than USB. As far as I know, Firewire also does not provide galvanic isolation so should have the same issues as any other copper connection which connects different systems with different grounding potentials. Otherwise, please provide a link, I would be interested in reading.

To prevent or solve ground loop issues (hum) you need to solve the root cause for that or need to provide galvanic isolation.
To solve EMI related issues, you should try shielded USB cables with Ferrite Chokes (on one or both sides).

I do the following to prevent EMI and ground loop issues. I use a dedicated power outlet in the fuse box to connect the computer and recording components.
My multiple outlets have both overload protection and a line filter.
If possible, I connect the devices that work directly together to one multiple socket to avoid different grounding potentials.
I only use well (up to triple) shielded quality cables from Lindy to prevent interference here as well.
I use quality components in the computer regarding mainboard, power supply and housing.
Maybe that's why I have never had any problems in this area.