(snicker) I’m not QUITE enough of a ditz to nuke metal cans.
Both these foods (and probably others that aren’t coming to mind right now) will do this whether covered or not (and will blow covers off unless they’re sealed tightly enough to risk a vacuum seal if the contents of the container cool enough).
Clam chowder is pretty viscous and will hold pockets of heated air/steam. Was the beef broth also thick and viscous? If the steam can’t escape easily it’ll build up pressure until, well, kaboom!
Some Healthy Choice meals include an “apple-and-goop” dessert that will jump over its enclosure, even without being covered. Through a lot of trial and error, I’ve discovered that you have to cook it longer, at a lower temperature.
I think that is true of a lot of things. I think the higher power/more efficient microwaves are too good at heating now. Butter is one that I have noticed. It used to be be 25 seconds in the microwave to mushify. But 25 seconds now will leave me with a molten hot mess- and I’m lucky if it doesn’t pop with pressure from the inside during the heating. So I recommend that you just heat everything like panache45, longer/slower with less heat/energy to prevent the popping explosions. [For the record, I tried to rewrite that last sentence 3 times, but it was just unavoidable…;)]
We do have a pretty high-power microwave (1250 watt, IIRC). I’d have been quite content with a more standard one, but DH went all Tim Taylor when we were shopping.
It’s not just new microwaves; I have an ancient Amana RadarRange that is older than I am and makes things like those described here explode (I always put a lid on stuff in bowls, so it really isn’t a problem, usually it is thicker stuff or stuff with sealed parts like beans, but stuff put on plates can explode too).