@martin-andersen This is exactly my issue with many off the shelf servers, motherboard is noisy environment. A top tier server will have usb coming off nice card like Pink Faun or JCAT, or perhaps some proprietary scheme.
I modded my server for second ethernet port, this port goes out to FMC, far superior to prior usb off motherboard into dac. Ethernet out was also superior prior to fiber conversion scheme I use now.