Now there is no trace of the PC’s digital noise in my audio chain. Installing the iDefender 3.0 absolutely solved the problem. I would even hear the PC’s EMI/RFI noise when the audio interface was turned off, USB cable connected, and speakers on. I’ve had this type of problem in the past related to HDD activity. In this case, the noise increased during network activity such as when multiple browser windows were active. The digital static noise coming from the speakers was not affected by the volume on the audio interface, only increased with the volume control on the speakers. I had taken all other measures to reduce noise and interference, including trying different USB ports, USB cables with a ferrite core choke on each end, installing ferrite core chokes on all power cables, making sure everything is on the same power circuit, and disconnecting all unnecessary devices that might introduce noise. Mainboard is a Gigabyte Designare, audio interface is a Focusrite Scarlett 18i20 (2nd gen), speakers are Yamaha HS80m. I’d been plagued with a low level digital static noise coming from my studio monitors for some time now.
