Ground loop issues with hardware synth

Hi, anybody had problems with ground loop noise after connecting a hardware synth with usb to the PC?

When i connect my synth with only midi cables, no problems with noise - no noise at all…

But when I connect it via USB there is a slight noise coming from my synth into the audiocard.

I’ve googled about it and found a USB isolator. Does anyone have experience with an USB isolator? Can it harm my synth or my PC?