Only to be used as USB, not with eigemen preamplifier

Today I get in the Black Turntable Omnitronic DD-2520.
I just misled by the good reviews here.
The device makes a really nice and solid impression - 1A Technics copy
Unpacking and connecting with joy, then a shock: It brummt- hum!
(I'm talking from the RCA output in phono setting, not the built-in USB output)
The USB was meant only as a nice addition because my preamplifier sounds better by a mile
and my computer is far away from my system.
I have two other players here, eg an old WEGA P4410, and there is no Nutzbrummen with exact the same
Compounds and components.

Conclusion for me: packing and back nerve.
Too bad, it would be determined to put only a small update on the device needed for a ground connection.
Then the Omnitronic DD-2520 would not be beat for the price.