Just to add more information, I tried USB in on XD05 Plus with my Android phone and there was no popping noise. I uninstalled the v5.0.0 driver and let Windows 10 automatically install a driver. After doing so, the popping noise was gone from there too. Now the only issue I have is the XD05 Plus being quiet. I also noticed that volume does not increase for the first 15°-20° of rotation after the click on the volume pot. Before the XD05 Plus got quieter, the volume increase happened much earlier (<5° after click). Do you think replacing op-amp would fix this issue? Is it possible the issue is elsewhere?