In message , "Dave Plowman (News)"
writes
Ground loops (to me) are usually a hum rather than buzz, so still don't
know what is going on.

And still don't know why the old X/O which has the same grounding
arrangements was OK. As I said, the only real difference is the old had
an analogue PS, while the new a SMPS.

Based on my experience with SMPS powered laptops in a pro situation,
this always sounded to me like shash of one sort or another from the
power supply, possibly induced into an earth loop.

It ought really to be queried with Behringer.
--
Bill