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Welcome. My name is ***** ***** would be glad to assist.
It sounds like the coil for the transfer mechanism is the noise you are hearing.
Do you hear the noise when the breakers are all on for the house?
If you have all the breakers off that activates the signal to start the generator. Then if the generator is off, the coil is trying to energize and transfer power form the battery off the generator.
That is the normal sequence.
The coil may be approaching its end of life and has some extra noise, but it will not hurt anything at this point, but may fail in the near future.
Power going to the house or any other location will not make a humming noise.
Let me know what is found,
Give me the make and model of the transfer switch please and I can get the specs and which coil may be humming.
The activation circuit on a Generator should not be wired to the main breaker, they monitor power at the transfer switch from the breaker at the main panel feeding power to the switch, so the specs will also allow the wiring sequence yours uses as well.
Appreciate the pictures, unfortunately the complete Model and Make of the unit is not visible.
Did a short search and with only partial doesn't show anything.
Full make and model would help.
Have the transfer switch manual and connections.
Looks like only one coil and solenoid inside the unit.
Need the information below:
1. Do you hear the noise when the breakers are all on for the house and generator in ready mode?
2. What size breaker in the main panel is connected to the Utility connections on the transfer switch?
Is it on or off when you hear the buzzing?