I've got a pretty substantial (well, substantial when using my Dynaco Mk III, noticeable when using my Trends PA-10.1D, and all but nonexistent from my Airist Heron 5) buzzing and random noise problem when using USB sources. Doesn't matter, Emotiva DC-1 or Modi 2U. Power off at the DAC and it's still there (at least it's still just as noticeable with the Mk IIIs).
At this point, I'm wondering where best to throw some money to clean up the gross USB noises. I'm open to suggestions here. Anybody have similar problems and found a solution?