I just unpacked my new D10 and it has the same low level hum audible through ear speakers that you reported. Even when not connected to a source or the power supply.
It goes away when you hold it in your hand.
I ran out of time to test it any further but it sounds like the only fix is grounding the housing.
What did you end up doing for this?
EDIT: Some quick diagnostics point to the issue being much worse with the power supply connected. It is also present with the unit in standby (off) and can be made better by wrapping the cable for the SR003 around your arm which changes the ground plane to some degree.
What headphones were you using as I tend to wonder if that’s where the issue is coming from? I intend to try it with different headphones but don’t have any to test with until Friday.