Hey, I have an APC Smart UPS. I'm in the UK so it's not really needed, but sometimes during storms it gets a bit clicky. Similar thing happens, the lights dim and the UPS clicks. All this is, is the UPS switching between battery and mains as it believes the power is too low or about to go off completely. Somewhere in mine there are settings to set the voltage at which it will switch to battery but I haven't touched that as it works okay. It sounds like the generator is not providing a consistent voltage. I’m not sure to be honest how long a UPS is meant to be able to switch between battery and mains when doing it constantly. In any case, if your lights are flickering your PC might switch off if not connected through the UPS.
I have a Synology nas which I am connecting to an Eaton 5e850iusb ups. Before I used to live in UAE. There the government is giving continuous electricity. The ups never made a sound and very rarely it would make a clicking sound and it would beep once. T