I am... not all that handy.
I was quite impressed with myself when I was able to tighten a fitting and get a water dribble to stop.
I know I've seen it happen at both 100% and "less than 100%" power.
The problem with doing any kind of test is that it's really intermittent.
I get the impression it's not a power problem because it has time to beep once before it shuts off. I too thought of overheating, but it seems more like it does it once early on and once it's "warmed up" it won't happen anymore (until it cools off again).
So far I've only run it off of shore power, haven't tried it on the generator. I need to run the generator for a bit sometime in the next few days just to keep it in shape, maybe I'll plan to make some popcorn at that time and see what happens.
I think I'll also call the manufacturer and ask about the beep-shutoff, since it seems distinctive enough that somebody ought to know what it means.
Thanks for the suggestions.