I had a device that did that noise and changed for other that... did it but at a lower volume. The most probable cause is a bad board wiring design that makes that sound and it is inherent to the DR1000 bad hardware design.
Some people reported they didn't hear it, but I've tested 5 units and all 5 did it. It is like old CRT monitors, that will sound similarity. For example, my Time Capsule, when it becomes hot it starts to make a similar sound.
No solution for that except throw away the device.