They not only can, they do. I have a Sanyo that is about 20+ years old
and is doing the same thing. I posted about it here a year or more ago,
and was told the mag tube gets weak. For now I am just living with it,
as it still does pretty well, I like the controls on it, and I just
haven't gotten around to switching the oven out. I have several others
that I have gotten from here and there for next to nothing (yard sales,
pawn shops etc.) and if/when the Sanyo gets too slow to be of any use,
I'll toss it and try one of the others. Low voltage to the unit can also
cause the problem, so you may check that. Unless you have a fancy
built-in that is part of a conventional oven, they are throwaway now.
You can buy a new microwave for less than the wholesale cost of a
replacement tube, or practically any other part on it for that matter.