We have an off grid home, solar powered 120v. While running the home on the backup generator (also charging batteries), the drum motor on the propane dryer has an increasing noise, then gets to a point where it trips the breaker on the generator, but the breaker on the manual transfer box (30 amps) and the 20amp breaker in the main panel are unaffected. I have check voltage and frequency at the dryer outlet with the generator running (dryer not plugged in the outlet), 119-121 volts and 59-61 hz which should be very acceptable. Also in a possible related sense, we have 4 ceiling fans 2 of which also get the hum situation but no issue with breakers.
Is your generator producing true sine wave, modified sine wave, or square wave output?
The motor's designed to work on sine-wave AC, which is what large generators are happiest producing, and which is generally the most efficient form since all the energy goes into the single frequency and can be easily drawn back out.
Square wave is easier for small alternators to produce, but has a lot of high harmonics which can cause resonance in motors, sometimes to the point of being damaging. Square-wave alternators may also be damaging to some electronics, for similar reasons.
"Modified sine wave" is a compromise between the two -- it adds another few steps between the most-positive and most-negative outputs. This reduces the harmonics to a level that most motors and electronics can handle safely. There are still going to be some harmonics, which may be made audible by the motor, but they shouldn't be strong enough to be damaging.
If you've got a square-wave unit, consider replacing it. If you've got a modified-sine unit and are still having trouble... well, switching to true sine wave will probably solve it, but you might want to get someone with expertise in this system to take a look at your set-up before you commit to that purchase.
It sounds like the inverter is producing a cleaner sine wave than the generator. Your TRMS meter might show 120 volts and 60Hz but isn't telling you the whole story. In other words, the sine wave is distorted with harmonics. The hum is telling you the story.
I am the one that posted the original issue. After research and consideration of what is happening, I believe that what is going on is that there is an imbalance in the way the generator/inverter is wired. I looked at the inverter/charger wire diagram and I am sure that the leg that feeds the charger is the same that is powering a larger portion of the home requirements, that being those kitchen lights, washer and dryer. The other leg is feeding a tv, a couple living room lights and a well pump that has a max of 1200 watts when running which should be a non-issue. We run the generator at night as most usage is lower at that time. I am going to swap the two feeds at the main breaker. Thinking is that what is being heard is the generator going into surge (the hum that starts low and increases) and then trips the breaker. A key thing happened is that I discovered the inverter generator was operating along with the circuits that run the dryer etc, and the twist lock had backed out some and there was no power to a portion of the home, that being the other leg from the generator...I thought the gen had an issue but it was the connection at the twist lock. I'll be back with the answer.