Question about EPOS Gsx 1200 Per

Greetings first 🙃 I have the following problem... I have a PC (power supply 850Watt from Corsair). The GSX 1200Pro Beyerdynamic 300mmx Gen 2 Everything works TOP. But now I have 2 x KRK Rokit 3 active speakers that I would like to use as monitors via the GSX. The problem is that when I switch the PC on or off, it clacks really loudly. That is one thing. The other problem is that as soon as I start a game I have a very loud beeping (no hum) on the monitors. It's a bit better since I put the ground loop isolator in between... but not completely gone... When no game is running I have no beeping from the monitors. And nothing from the headphones either. Thanks 👍