Call Progressive. My hard wired 30 A EMS had the same symptoms from day 1. It always displayed 4 volts higher than the actual voltage. They told me how to adjust the unit to read the same as the input voltage. Maybe yours just needs this adjustment or maybe its bad. Can't help with the hum. Hope this helps
Norman & Janet with Minnie the Weiner Dog
2005 SunnyBrook 38 BWQS 5th Wheel (stationary in FL for snowbirding)