You need to be able to connect the refaceDX directly to your Mac (or learn more about the beatstep pro — we know nothing about it, but it is not outputting what it receives).

The noise you are hearing could be simple ground noise. USB ground noise is usually described as a ‘high pitched zinging’ noise. You can hear it is related to computer CPU activity... ask your computer to do an internal search, the timbre change of the noise will coincide with CPU activity. (This is one clear way to know if it is USB ground noise). Solving the issue begins with proper identification.

_ Determine if this is, indeed, USB ground noise.
_ Try plugging items in to a single Power strip... or sources that originate from a single source. All connected items are apart of the grounding including your speakers (which are reproducing the noise). Consider everything you are using as being *connected*. So if you have multiple wall outlets where they might be on different lines in your building... this can be enough to cause hum.
_ Try running on batteries. Certainly running the computer on batteries will solve the issue but be certain you don’t lose functionality when it runs on batteries (mileage varies).
_ Try running the refaceDX on batteries.
Ground noise typically happens when several interconnected electrical devices disagree on the current flow...

It is sometimes really easy to fix (changing how things are plugged in, DI box with ground lift etc.) and other times it’s a warning of a larger issue. Diagnosis should be handled in person by a qualified technician.
That said, ask in your area of the world what the simple solution is...

Hello!
The noise isn't high pitched, although it is not the 50 or 60 Hz hum noise we can encounter in a studio, but I did put my imac doing some activity and i didn't noticed any change in the timbre of the noise.
I have more than a dozen equipments connected in my studio and i never had ground noise issues.
I did connect them in to the same power strip, although that doesn't matter much because all the wall outlets in my studio (the ones for connecting sound equipment), come from the same power line in my house.
The imac can't run on batteries! And, honestly, I don't think that running the reface dx on batteries should be the answer.... Any other suggestions, including forgetting the dx has a usb connection or even a possible return of the reface to the store?

As for the polyphony that isn't working via midi through the beatstep, i'll investigate on the beatstep end and see if i find anything.

thanks

The noise isn't high pitched, although it is not the 50 or 60 Hz hum noise we can encounter in a studio, but I did put my imac doing some activity and i didn't noticed any change in the timbre of the noise.

Then the noise is unlikely a USB ground issue.

Without hearing it and with no real description, it’s impossible to say what the noise is.
How are you getting the reface audio into your computer?