"Joseph Meehan"

My guess would be that the OP's mixer (a moving part that sort of
stirs
the microwaves as they go into the box may have failed.

Agree. Did not even think of that. It would cause the uwaves to heat
unevenly and overheat some spots. I doubt that the total output has
increased :-)

In my old Panasonic (which I can hardly lift anymore), you can see the
shadows dance around from the uwave deflector.

BTW you are right that that today's are not designed to last as long.
They also are better in some ways, but longevity is not one. They are
generally lighter weight, and more efficient as well as they tend to cook
a
little more even.

Again agree. Nothing wrong with making the appliance lighter. Saves on
materials and sore backs :-)

Too many improvements of this sort are unfortunately made in the wrong
places, resulting in broken silly bits that ruin the whole appliance.

Rich