On September 10, 2017 at 11:00, mark65 said...
Run a long extension cable through the house and connect the 2nd rack to the same outlet as the first rack. If the hum goes away it's a power phase issue. So moving the breaker to the same phase should fix the issue.
In the future, I suggest not having two racks. If it's an absolute must, you should be using fiber to connect the two.
The NEC requires bonding the racks but most people don't. IIRC, it's Article 25 or 725.
