i have this issue that happens with two different steinberg UR44 (my dealer was kind enough to replace the first one i received.
when i plug my electric guitar (fender strat + ) througt my multieffect (Johnson J-Station) to th UR4 (line input )
there is a loud 50Hz noise that makes this setup unusable.
When i replace the UR44 power supply with another one i had by my own (yamaha PA100-S) : no more noise !
As i said, i have this issue with two different UR44 and power supply
i’m considering send it back again and ask for a refund unless there is a solution to this.
Thanks for your help.