High pitch electric noise from Krome output

[ymusic]

Hi there! I have a Korg Krome 73

If I turn it on, there is a really high pitch electric sound, could be heard even without connecting it to speaker (attached) http://sndup.net/vr9z <<< I recorded this through my audio interface, so it also presents on the line out.

After several minutes, the noise kind of gone. But it is still presents on the line out (again from my audio interface) http://sndup.net/p582

I ruled out ground noise because it is a seperate issue. I have purchased a passive DI box and the noise ground is gone.
But now I have this issue. Although no one notices on stage, I am simply annoyed by this high pitch electrical noise on stage.

Does anyone have a clue how to tackle this? Thank you so much