While cleaning my microwave I noticed the paint under the tray is starting to flake away and it looks kinda rusty underneath. Is this a danger in any way?
The paint flaking off isn’t a problem but the metal underneath rusting is. Tiny little bits of surface rust (like say,spots that are smaller than the holes in the mesh on the door) aren’t a problem but once the metal starts rusting through and you get larger damaged spots then the microwave can start to leak radio waves and you can end up with uneven heating and maybe the heating of the microwave case itself due to eddy currents going through the uneven metal. At some point it may even start arcing.
Depending on how big the rust spots are, it’s probably time to start looking for a new microwave.