Glad to receive your reply:“It’s still grounded or you wouldn’t have a ground loop Typically everything is connected by interconnects, etc. which tie the grounds together.”
If everything is grounded together, why does my DS output ground noise? BTW, that noise comes out even I switch it off by switch at back but connect it to power bar. very strange. Without DS, my system is very quiet.
Here is more detailed info than you might want/need, but learning how to deal with groundloops will serve most of us well: http://www.jensentransformers.com/an/ts_guide.pdf Remember Bill Whitlock is selling transformers to help with the problem, but his information is correct and useful, and he forgotten more than most of us will ever know about these things.
Jesnsen Transformers has a lot of other good info at http://www.jensentransformers.com/apps_wp.html
I suspect that whatever is your USB source is plugged into a different leg of your power than the rest of your audio system.
Still if lifting the ground connection on the DS fixes your problem, I’d just do that… There’s nothing inside the DS that could likely work loose or fail to cause this. The DS is probably working as designed.