Do you think it's an electrical squeal or just the fan turning on? When you use a number off 12-volt items (lights, furnace, water pump, etc), the converter will convert 110v to 12v when on shore power so that you don't run down your battery, as the unit warms up it has a fan that cycles on/off to keep it cool.
An electrical squeal is bad, the fan turning on to cool down the unit is no problem.
2013 Jayco JayFlight 26RKS
2013 Ford F150 Ecoboost FX4
2003 Coleman Bayside / 2011 Jayco Jayfeather X20E -- RIP
2012 Tacoma Sport DCSB / 2013 Tundra SR5 - RIP