If your microwave acts funny when the generator is running, that's another indication of high voltage and frequency. So are clocks that gain time.
You might also watch your DC voltage with the generator running. The converter/charger probably puts out greater than 14.0 volts if the source voltage is too high. It's ok for the charge voltage to be high while the batteries are low, but once they begin to charge up the voltage should fall to about 13.6. If it doesn't, the genset voltage may be high.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL