Suddenly today one of the transfer switches at the foot of the bed in our '96 U295 started making a loud clattering noise. We turned off the inverter immediately. I took the covers off both switches and when the inverter was turned back on, the contacts on the inverter input side of the second switch were sparking and causing the clatter. I was going to bypass the switch so we could keep the residential refrigerator running, but first I turned all the breakers off in the sub panel fed by that switch and started to flip them back on one by one after turning the inverter back on. Two of them were fine but the third one caused the arcing. I replaced that breaker in the panel and turned everything back on and it is all working. I'm not sure why a bad breaker would cause the switch contacts to act that way. but it did. Maybe this will help someone else?
Nice troubleshooting!
What was on that third breaker that you found causing the problem?