Quote Originally Posted by Clive View Post
You have a ground loop caused by your power brick being earthed. Find a way to disable the earth on it, with a laptop this SHOULD be safe. I have the same with my laptop. I created a 6 inch extension lead with no earth connection. Or use a galvanic isolator on the USB.
I can easily remove the eart and you are right, it should be fine. The annoying thing is that the laptop itself gives a slight hum without the power supply plugged in. Any suggestions for a galvanic isolator for the USB?
My whole grand Digital Plan is falling at the first hurdle here