Smart-UPS 1500 - False site wiring warning

[OVERKILL_apc]

I have two of these units at the house, both are environment pulls from upgrade jobs. Both work fine. 

However

The one unit constantly displays the "Warning State: Site Wiring" and has a bit of a transformer hum to it. The other one, if plugged into the same outlet, does not display the warning, nor do any of my other UPS's. The other one is also silent (no hum). 

I was going to try directly grounding the chassis and see if that has any impact, just curious if anyone has run into this before? I assume it's an internal wiring issue with the unit that's causing it not to sense that it is grounded. 

[BillP]

@OVERKILL_apc 

What is the exact model, serial number, and firmware version of the UPS? If the UPS is a SMT SmartConnect UPS or SMTL you can disable the site wiring fault using the LCD panel. 

[OVERKILL_apc]

Model: SMT1500

Serial: AS1132111365