Thank you all. I have several things to try now. Some are from checking the PreSonus site. It is not complete, and they are in no particular order.

1. Replace the USB cable.
2. Make sure it's not plugged into a USB 3 socket.
3. Isolate the PC. (I may try a ground lift there.)
4. Reroute control, power, and signal lines as appropriate.
5. Replace the sound card. (That would be kind of okay since I'd like to upgrade to one with a S/PDIF output so I could use the Focusrite(?) VRM speaker emulator with my headphones.)

There is more, but this will keep me busy for a while. I'll keep you posted.

R.


"My primary musical instrument is the personal computer."