I've never noticed a hum from our P.I. 50 amp hard-wired unit - but it's installed behind the electrical panel in the bottom of the buffet. When the weather got hot this summer, we started having problems with the system cutting out for low voltage (below 104 volts)... always on one leg. This happened at two different parks. Upon investigation, I discovered that both ACs - one 15K, one 13.5K - we on the same leg of the RV 50 amp service. I juggled breakers and put them on separate legs and haven't had a problem since. We've not had high voltage issues, so can't speak to that.
Rob