Help/advice please - buzzing speakers

[W1tchseason]

Hi, I hope this is an appropriate forum to post this.
My main setup uses a focusrite Scarlett with KRK Rokits and sounds great.
Recently I decided to set up a secondary system in another room using my laptop, a Scarlett Solo, and my two minirigs as monitors. That also sounds great - until I plug in the power cables for the minirigs, at which point they start humming/buzzing/fizzing. I'm guessing there's an earth loop somewhere - but how do I solve that?
The laptop has three usb ports. One is connected directly to the (bus powered) sound card, nothing else. The minirigs are connected to the solo with good quality shielded cables.
Another usb port is connected to a powered usb hub that has its own mains adaptor, and I'm drawing power for the minirigs from that as well as connecting my mouse and external drives to it.
If the minirigs are running on battery power it sounds fine, but when I use power from the hub they emit a buzzing/fizzing noise.
Any suggestions as to why, and how I can fix it?
Thanks in advance

[megreenway]

Hi, Buzzing is usually caused by a ground loop. My old Yamaha Steinberg interface had this issue most of the time Revesring the US Style 2 prong AC power connecter in the outlet fixed the issue if not I would add a ground wire to the metal case directly to a known ground.

hope this helps.

[W1tchseason]

Thanks, I'll try that.
J.