Sigh, it's almost like I had this conversation before.
My audio equipment is not connected by USB. It's connected by optical (TOSLINK) to an external DAC. TOSLINK is not great, but it shows that it is not a USB noise problem.
I got rid of the noise via the method I described in the original comment? Moving my audio equipment to separate power strip on a separate outlet. It didn't totally remove it, but made it quiet enough to deal with.
Don't mind them. I've had a similar thing happen, but with power line Ethernet. In your case however, I'd be at least a little concerned about the building wiring.
