Ron Hardin wrote:

Adrian wrote:
Then you'll find you get enormous AC hum when you connect to your computer,
owing to a ground loop. Put a Radio Shack ground loop isolator in that line
(cat 270-054). I keep a bunch of them around to isolate every different thing
that's plugged in on AC mains.

Is that true even if I utilize the USB link into my Notebook?

Yes, it's a problem in the connecting audio cable. The computer and the audio components
don't have quite the same idea of what ground potential is.

That's the traditional reason for 'hum loops'.

In this case the problem is made worse but the use of switching power supplies (certainly in the
computer) and in some audio gear (I'm fairly certain the Behringer model mentioned also has one).
These swiching power supplies have filters on the ac power input that injects a noise current
into the ground conductor. This messes up your grounding arrangements very effectively.

Graham