Using a Sonore Ultra Rendu and now the Optical Rendu, I get a thump when switching to the USB input.
Also, with the music paused, I can hear quieter thumps with each volume step.
So far I have tried an Audioquest Coffee USB as well as a generic no name cables.
Is this a cable problem or something else?
With respect to the volume change noise, Paul explained “there is a small “thump” and change when the volume control changes quickly. It is in the nature of the Gain Cell technology. When we checked the units sent to us we saw/heard the thump
but it was so low as to be inconsequential one our systems. Still, we worked to get it as low as possible realizing that in the case of a few folks the thump was audible in their setups.”
Thanks, but I don’t hear it with the USB disconnected.
Minor issue anyway, but wanted to point it out.
The major problem is the big thump when selecting USB.
I understand, but thought the information about the little volume change noise might be of interest to you and others. 
I unfortunately do not know anything about the USB thump. Is the thump present only when a Rendu is in the mix?