If you have the ATS, it could have very well been the ATS doing the knocking and sputtering not the genset. When the ATS trips, it tries to reset. But with the draw on the genny because the ACs are trying to kick on at the same time as the switch is trying to reset, the switch can't reset. So it keeps trying, and makes a grinding/knocking/buzzing sound. I am willing to bet that is what happened. And my understanding is that once this happens to your ATS, it is never quite the same again; it is prone to keep doing it as it is weakened. I know cause it happened to me, and it seems when the ATS gets hot it becomes prone to tripping out. I have been told that the ATS that forest river uses is a lower end model, and replacing it with a better one is recommended. Still researching that. But take a look at your spec sheet and see if you have the ATS. If you do, I am pretty confident that the ATS kicking out is what you experienced.
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