Thank you. I just solved it. I have a USB to optical converter in another system, so I set that up with a short USB cable and long optical cable to the DAC. Now, no static. It seems I have some RF in my listening room that the longish USB cable was picking up. I should have realized this as a recent power cable upgrade made a nice difference, probably in part because of the RF shielding these power cables have.
Thank you for your help.